You can work at McDonald's and still become a millionaire, a financial psychologist says

Brad Klontz was drawn to financial psychology after the tech bubble burst in the early 2000s.

Klontz had tried his hand at stock trading after seeing a friend earn more than $100,000 in one year. But he felt immense shame after the market crashed and his investments evaporated.

He set out to discover why he took such risks and how he could behave differently in the future.

Today, Klontz is a psychologist, a certified financial planner and an expert in behavioral finance. He is a member of the CNBC Financial Advisor Council and the CNBC Global Financial Wellness Advisory Board.

In his estimation, psychology is perhaps the biggest impediment to people's financial success.

Klontz's new book, "Start Thinking Rich: 21 Harsh Truths to Take You from Broke to Financial Freedom" — co-authored with entrepreneur and social media influencer Adrian Brambila — aims to break down the mental barriers that get in the way of financial freedom.

CNBC chatted with Klontz about these "harsh truths" and why he says people earning a McDonald's salary can still become millionaires by tweaking their mindset.

The conversation has been edited and condensed for clarity.

Greg Iacurci: Why is psychology important when it comes to personal finance?

Brad Klontz: The basics of personal finance are actually quite simple. Financial literacy has its place, but I think it's mostly [about] psychology.

Here's my argument for that: The average American, the two biggest problems we have is we spend more than we make, and we don't save and invest for the future. And I've literally yet to meet an adult who doesn't know that they shouldn't do those two things. So, everybody knows it. Nobody stays broke because they don't know the difference between a Roth IRA and a traditional IRA. That's not the problem we have.

It's not really about the lack of knowledge. I think it's all about the psychology. 

GI: So how does people's psychology tend to get in the way?

BK: The biggest impediment: money scripts. Most people aren't aware of their beliefs around money. And there's a whole process for discovering what those are. Part of it is looking at your financial flashpoints: these early experiences you have around money or that your parents have had, or your grandparents have had. People tend to repeat the pattern in their family, or they go to the extreme opposite. 

GI: You write very early in the book that there's a difference between being broke and being poor. Can you explain the difference? 

BK: We're talking about a poor mindset.

Being broke means you have no money. I've been broke, my co-author was broke, our families have been broke, a lot of people have been broke. We differentiate between being broke, which is a temporary condition, hopefully, to a poor mindset, which will keep you broke forever.

It's not really related to money, because I know people who make six figures and multiple six figures, and they have a poor mindset. We all know stories of people who win the lottery, or they win a big sports contract or music contract, and then all of a sudden [the money is] gone. Why is it gone? They have a poor mindset. That's the distinction we make.

GI: Does this suggest that people, no matter their socioeconomic circumstances, can lift themselves out of poverty if they adopt a rich mindset?

BK: Yes.

GI: Is that one of your "harsh truths"?

BK: Yeah. We frame it in different ways based on the [book] chapter titles. For example, "It's not your fault if you were born poor, but it is your fault if you die poor." That's a pretty harsh reality that we're throwing in people's face.  

GI: What is a rich mindset?

BK: It's an approach to life and an approach to money.

Some of it goes against our natural wiring. There's a future orientation. You have to have a vision of the future. A poor mindset [is] really focused on the here and now, not really thinking about the future. And if you don't have a clear vision of your future, you're not going to save, you're not going to invest, you're not going to live below your means.

A rich mindset puts an emphasis on owning their time versus owning a bunch of stuff. A poor mindset, as we describe it, [is] very willing to trade time for stuff.

GI: What do you mean by that?

BK: A poor mindset is like, I want this fancy car. And I'm very willing to work an extra 10 hours a week so I can drive that car around. And the problem with that is that mindset goes everywhere: "I'm gonna buy the biggest house I can get, I'm gonna get the nicest clothes I can get, a big watch." And then people have no net worth. They're not saving any net worth.

GI: I thought this was a great line. You write: "The belief that rich people are big spenders could be one of the most destructive beliefs about money ever."

BK: I've done research on this. In one study, we looked at a group of people who [each] had about $11 million in net worth, and we compared them to a group of people who [each] had about $500,000 in net worth. These people had almost 18 times more money. And what we found is they only spent twice as much, on their house, their vacation, their watch and their car.

They had the money to spend 18 times as much, right? The people who are the wealthiest, when it comes to money scripts [they] have money-vigilant money scripts, which is the belief that it's important to save.

The ones who are the flashiest spenders [have] "money status beliefs." They had lower income, lower net worth. They're more likely to come from poorer homes. It's like, "I'm gonna show the world I've made it." But that keeps you broke.

And I had it, by the way. All these insults about this poor mindset, I had it all.

GI: So what is the No. 1 thing people can do to save themselves?

BK: The first part is embracing some of these harsh realities: Your political party is not going to save you. Your corporation doesn't care about you. Your beliefs about money are keeping you poor.

These are all meant, in different ways, to just help you shift from an external locus of control to an internal locus of control: The outcomes I've been getting in my life are because of me. It's because of what I did, what I didn't do, what I didn't know. It's a difficult mindset to grasp.  

You need to wake up to the fact that it doesn't matter who the president is in terms of your financial freedom. None of them are going to make you financially free. They're not going to send you a check. Your company? They don't want you to be financially free. The replacement cost for you is really high. Your teachers can't teach you to do that. They can teach you history and English. But they're not financially free themselves.

The bottom line is, you have to do this yourself.

Then the next question is, well, what am I supposed to do? And that's where we want to get people, because that's a much easier answer.

GI: And what is the answer?

BK: The answer is really, really simple.

Here's the rich mindset: $1 comes into your life; you are going to put a percentage of that towards your financial freedom before you do anything else.

You can work at McDonald's your entire life and be a millionaire if you have that mindset.

GI: What is the percentage people should be aiming for?

BK: It just depends on how rich you want to be and how fast you want to be rich. That determines the percentage. You'll hear personal finance experts say you should be saving and investing at least 10% of everything you make. I advocate for 30%; that's what I shot for, just because I think it helps you get there faster.

And people are like, "Oh my gosh, 30%." Well, it's real easy before you get your first job if you have this mindset. It's real tough if you've designed your entire life around 100% of your paycheck. That's where you have to make cuts.

We have a chapter on cutting expenses. It's called "Get a roommate, get on the bus, get sober, get bald, and get a side hustle or shut up about being poor."

We [hear] this all the time: "I can't afford to invest." We're calling bulls--- on it. Yes, you can.

We looked at the average amount that Americans spend on rent, on cars, on going to the salon, and on alcohol. Two thousand dollars a month is average rent; if you have a roommate, it cuts it down to $1,000. Just that alone, if you invested the difference, in 25 years you'd have $1.3 million. Now, if you had three roommates, it would go all the way up to $2 million. Just think about that. You now are a multimillionaire just from that, doing nothing else. And by the way, that's average market returns.

But then when you add in: Take the bus, stop drinking alcohol, shave your head? [That's] $2.8 million in 25 years.

GI: If you do all those things?

BK: If you do all those things. That's just one roommate, riding the bus, not drinking alcohol and not going to the salon — watch YouTube [or] get your friend to cut your hair. The richest people I know, this is the kind of stuff they do. And yeah, $2.8 million.

I would say to you all: That sounds terrible.

OK, so why don't you just go ahead and invest 30% of every dollar you make? Then you don't have to do any of that s---. If that's your mindset, it's impossible for you not to become a millionaire. Unless you do something stupid, like take your investments and do something crazy.