A lot happens between the day you come into this world and the day you leave it. If that sounds like one big understatement, then tell me this: Why do so many people lament that life is short?

Sure, some don't mean anything by it; it's just their way of saying you have to make the best of it. But others say it in a regretful way, like they missed out on something. I hear that sentiment often enough from fellow baby boomers: "It's like I went to bed a young man and woke up looking like this," they exclaim, "What the heck happened?"

I often wonder why I've never felt that way. To me, life has always felt long and full of twists and turns and possibilities.

The perception of time passing is a subjective thing. And it relates very much to how you live your life.

You see, what separates successful people from everyone else is surprisingly little. Certainly less than you might think. I'd even go as far as to say that the biggest difference between successful business leaders and the pack is that the leaders know there really is no difference.

For the most part, success isn't predetermined.

Sure, some are born with privilege, but that's rare. Most of the successful people I know started with nothing. They're self-made. What really distinguishes them is that their reach always exceeded their grasp, as Robert Browning so aptly put it.

They always wanted more out of life, so they always strove to achieve more, at least until they felt they'd had enough. Sure, they also had the guts to take risks, but that's really no different from being willing to get on a really scary ride at the amusement park.

Just think about it. If you go to the amusement park and you're only willing to go on the boring rides, you can sort of sleepwalk your way through the whole thing. Then when nighttime comes, you wonder what all the hoopla was about. But if, on the other hand, you challenge yourself, face your fear, and get on those terrifying rides, you'll end up with loads of wonderful memories of an eventful and fulfilling day.

Life is the same way. So is your career.

Here's a great example. I've always been a slow starter. No, I'm not slow; it just takes me a while to figure things out. While I was hired into my first engineering job with great fanfare and expectation on the part of my employer, it took years for me to really start to shine. Even then, I got bogged down in middle management for quite a long time. And that just wasn't acceptable.

So I quit and tried something different: sales and marketing. It wasn't until my mid-30s that I finally reached the executive ranks. I could have milked that until retirement but you know what? I still had some other rides I wanted to try, if you know what I mean. So here we are. Am I done? No way. Not yet.

Satisfaction and success are subjective.  

Lots of people I know have had second or even third acts in their careers. Many have gone the entrepreneurial or venture capital route after decades of climbing the corporate ladder. Lots of famous people weren't satisfied with their original careers, either.

John Grisham was a criminal lawyer and a congressman for nearly two decades before his first book was published. Even then, he continued to practice law until his second book, The Firm, became a hit. Ronald Reagan was an actor for decades before getting into politics. It's a long, long list.

Look, I'm not going to sit here and tell you that anyone on planet Earth can be wildly successful. I know that lots of authors and coaches suggest they can help anyone unlock their inner potential to succeed. I'm not one of them. But don't think for a minute that anything is predetermined. It has more to do with you than anything else.

Mostly, I think it comes down to what drives you. If you're content with who and what you are, that's great. Stick with it and call it a day. If you're not, the message here is a simple one. Keep getting on those rides until you've had your fill. Then, when nighttime falls, I guarantee you'll feel like you've had one hell of a fun day at the amusement park.

And you'll never wake up wondering where the time went--or feeling like life is too short. It'll feel just about right.