Of the 12 billionaires I've met (yes, I keep count), Mark Cuban seems the most relatable. Partly that's because he's entirely self-made. 

But also because, like most, he believes success comes down to effort and ability. And because, like most, he hates meetings. And because, as most of us like to think we are, he's a genuinely good person

As a result, Cuban's advice often seems more applicable to the average person hoping to achieve success in their chosen pursuit. He's done what we hope to do -- and as a result, he knows what really matters.

Like:

1. Sales Skills Matter

What would Cuban do if he had to start over again?  

"I would get a job as a bartender at night and a sales job during the day," he says, "and I would start working. Could I become a multimillionaire again? I have no doubt."

The reason is simple: Everyone needs to be able to explain the logic and benefits of a decision. To convince other people an idea makes sense. To show investors how a business will generate a return. To help employees understand the benefits of a new process.

To motivate, and inspire, and lead.

Because sales skills are, in essence, communication skills -- and communication skills are critical to any business or career.

Which means spending time in a sales role, whether formally or informally, is an investment that will pay off forever.

2. Constant Learning Matters

What does Cuban feel will drive the next wave of business change? Artificial intelligence.

If you don't know A.I., you're the equivalent of somebody in 1999 saying, "I'm sure this Internet thing will be OK, but I don't give a shit." If you want to be relevant in business, you have to, or you will be a dinosaur very quickly.

If you don't know how to use it and you don't understand it and you can't at least at have a basic understanding of the different approaches and how the algorithms work, you can be blindsided in ways you couldn't even possibly imagine.

That's not just posturing; Cuban put his mind and money where his mouth is. He frequently recommends books about artificial intelligence, like Competing in the Age of AI: Strategy and Leadership When Algorithms and Networks Run the World. And he's committed millions to expand his AI Bootcamps Program, an organization that teaches artificial-intelligence skills at no cost to high school students in low-income communities across the country. 

"The world's first trillionaires," Cuban says, "are going to come from somebody who masters A.I. and all its derivatives and applies it in ways we never thought of."

While most of us don't dream of becoming a trillionaire, no matter what your industry, no matter what your pursuit, things always change. Things always evolve. 

They key is to know how to change with them. 

Which you can only do if you're constantly, actively learning. 

3. Being Nice Matters

Think about the best boss you ever had. Odds are they were demanding. They had high expectations. They may have provided occasional doses of tough love.

But I'm guessing they were also nice. Not soft, not lenient. But even so, nice.

That's a lesson Cuban had to learn. As he says:

I went through my own metamorphosis. Early on in my career, I was like bam, bam, bam, bam, bam -- I might curse. I might get mad. I got to the point ... I wouldn't have wanted to do business with me when I was in my 20s.

I had to change. And I did. And it really paid off.

One of the most underrated skills in business right now is being nice. Nice sells.

He's right. When you're nice, other people are more forgiving of your mistakes. Other people are more tolerant of your lack of experience or skill. Other people are more willing to work with you, help you, encourage you, and, if you're a leader, follow you.

4. Finding Your Passion Doesn't Matter

Ask 10 people if they love what they do -- ask 10 people if they've found their passion -- and at least eight will likely say no.

Sound depressing? 

Not to Cuban, who feels "follow your passions" is "one of the great lies of life," and is the "worst advice you could ever give, or get."

According to Cuban, passion doesn't come first. For Cuban, passion comes later

A lot of people talk about passion, but that's really not what you need to focus on.

When you look at where you put in your time, where you put in your effort, that tends to be the things that you are good at. And if you put in enough time, you tend to get really good at it.

If you put in enough time, and you get really good, I will give you a little secret: Nobody quits anything they are good at, because it is fun to be good. It is fun to be one of the best. But in order to be one of the best, you have to put in effort.

So don't follow your passions. Follow your effort [my italics].

That's why Cuban completed Amazon's machine learning tutorials. That's why he spent time building his own neural networks. That's why, at one point, he kept the book Machine Learning for Dummies in his bathroom.

"The more I understand A.I., the more I get excited about it," Cuban said

In short, Cuban didn't discover a passion for artificial intelligence. He developed it.

Oddly enough, according to a 2014 study published in the Academy of Management Journal, that's how the process often works for entrepreneurs. 

While it's easy to assume that entrepreneurial passion drives entrepreneurial effort, research shows the reverse is also true: Entrepreneurial passion increases with effort. The more work entrepreneurs put into their startups, the more enthusiastic they get about their businesses.

As they gain momentum, gain skill, and enjoy small successes -- even if those "successes" only involve ticking off items on their seemingly endless to-do lists -- their passion grows. 

Can passion spark effort? Absolutely. 

But effort can also spark passion, which in turn sparks greater effort, and greater passion, until one day you wake up and realize you are doing what you love.

Even if it didn't start out that way.