There’s an old saying that a leopard can’t change its spots. It means that people can’t change their inner nature. Since it comes from the bible and is still around to this day, this bit of conventional wisdom has clearly stood the test of time. The only problem is that it isn’t true. Not even close.

Every successful executive and business leader I know has had to face his limitations and make big changes at least once during his career.

Don’t get me wrong; it isn’t easy. But make no mistake. People can and do change. And I mean real behavioral change, the kind that makes people say, “It’s like she’s a different person,” and actually mean it. Here’s how it works.

Three basic biological functions determine your behavior. You’re born with DNA; you learn and develop neural pathways through experience; and your behavior is chemically reinforced by neurotransmitters like Dopamine and Serotonin. It’s all very complicated.

What isn’t complicated is this. You start out life with nearly a clean slate and pretty much anything you do after that is reversible, under certain conditions:

You have to feel the need to change.

The other day I was discussing the shortcomings of a certain high-profile CEO with a colleague of mine who opined, “One has to want to change.”

If only it was that easy.

Most behavioral characteristics you’d want to change, like the career limiting or self-destructive variety, are created in response to adversity, crisis or trauma when we’re young. They’re designed to manipulate our environment and keep us safe, and they’re reinforced countless times throughout our lives.

Unfortunately, what works for children doesn’t work so well in the adult world. Sooner or later, our issues get us into trouble.

Steve Jobs once talked about the devastating loss of being ousted from Apple, an event that was influenced by his toxic management style. "I didn't see it then," Jobs said, "but it turned out that getting fired from Apple was the best thing that could have ever happened to me. It was awful-tasting medicine, but I guess the patient needed it.”

Getting fired from the company he loved was a crisis for Jobs. And he responded by addressing the issues that caused it. He changed, not because he wanted to, but because he felt he needed to. Had the crisis never occurred, that wouldn’t have happened.

You have to have courage to face your fear.

I used to work with two CEOs that were remarkably similar. Both were smart and capable. Both were introverted and geeky. Both were controlling micromanagers. Both achieved senior executive positions with established companies but, when it came to running their own start-ups, one made it big while the other flopped miserably.

Why the difference? When it was smooth sailing, both did well. But in the face of adversity, one chief executive had the courage to face his fears and, in time, overcome them. He took responsibility for his actions. He owned them. And it paid off in the long run.

The other CEO let his fear and dysfunctions get in the way of his decision-making. Over time, he and his company spiraled down, seemingly in lockstep. Since he lacked the courage to look in the mirror, he still blames his failure on external factors.

You have to make the commitment and fight.

Most people just don’t get how change works. They think it’s event driven. One day you’re one way, then something happens and, poof, you change. That’s just a myth. Sure, events may trigger the need to do things differently, but that’s just the beginning of a long process.

First you’ve got to peel the onion and figure out what’s going on. Sometimes you think you’ve gotten to the heart of the matter, only to find that it was just another layer. It’s also a nonlinear process, meaning sometimes you move forward and other times you fall backward. It can be really frustrating.

That’s why change requires a commitment of time, a willingness to sacrifice, and the faith to persevere. Sure, it’s an arduous process, but so is anything important in life. Everything worth achieving is worth fighting for. And you know what? When you stop fighting, you stop changing, and you stop achieving.