In 2006, Dharmesh Shah founded HubSpot with his friend and MIT classmate Brian Halligan. Five years later, HubSpot served over 5,000 customers and ranked No. 33 on the Inc. 500. They didn't stop there: HubSpot went public in 2014 and today boasts a market cap of over $17 billion.

Shah? He's clearly living the entrepreneurial dream.

So you could be forgiven for thinking it sounds odd that Shah recently created WordPlay, a web-based word game -- think Wordle, except you can also do things like challenge friends and play group games -- that has been played by over 6.5 million people and averages 3.5 million weekly users. 

That is, until you understand why the founder of a $17 billion company created a word game. 

Shah loves word games. Like millions of other people, he played Wordle. 

Earlier this year, his 11-year-old son was taking a 16-week Python programming course. Learning is always more fun when what you can do with what you learn sounds fun, and Shah wanted to find a way to keep him motivated and excited. 

"One of the things that keeps me up at night," Shah says, "is how I can teach initiative and drive to my son. He's going to have it much easier than I had growing up. How do I ensure he adopts a growth mindset and builder's mentality?"

So one Saturday night, Shah built an app called FirstWord, a math-based tool that predicts how good a Wordle first-word guess might be. (To make the process more interesting, he decided to give himself only 24 hours to code and launch it to the public.)

The next morning, he showed the game to his son and said, "Look at what I built in Python. We're going to launch it together." Within hours they watched thousands of people around the world play a game built in less than a day.

Then, in classic entrepreneurial fashion, he spotted an opportunity. Since Wordle can be played only once every 24 hours, and practicing once a day isn't a particularly effective way to improve any skill, Shah decided to create a word game inspired by Wordle that built on FirstWord, and WordPlay was born.

"Cool," you might be thinking. "But doesn't the co-founder of a $17 billion company have better things to do?"

Yes. And no. 

For starters, HubSpot itself was an "accidental" company. Shah started a blog, OnStartups, as a thesis project in grad school. According to Shah, without that blog he and Halligan would probably not have had the idea for HubSpot.

And while having a plan is great, as Shah says, "Sometimes you do things that feel right. As long as you're learning something, enjoying it, and bringing value to people, it's probably worth doing."  (Or as Steve Jobs said, "Sometimes you can only connect the dots by looking backward.")

And then there's this. What does Shah say when asked why he still codes?

The answer is simple: It's what I love to do, and it's one of the few things I think I'm good at.

It's funny, because if you're a best-selling writer, you keep writing. If you're a world-famous musician, you keep playing. But if you're a good software developer, you're expected to move into management in order to succeed, and writing code is seen as a "waste of time." 

I see it differently. To me, success is about honing your craft over years and years, and being one of a very few with a specific mix of skills, versus being a "manager," of which there are millions.

Many of whom, I imagine, Shah feels are much better managers than he will ever be.

While for many success is determined by external factors like numbers, metrics, or public profile, a better definition of success is whether you get to do work you enjoy. Work that leaves you feeling fulfilled, satisfied, and happy. Work that provides opportunities to learn. Work that gives you something to look forward to. 

Honing your craft to develop the specific mix of skills that you want to develop.

Embrace other people's definition of success and, with time and effort and persistence, you can certainly build a "successful" business or career -- but the process may also leave you feeling hollow.

The beauty of starting a business or side hustle or path you find interesting is that you get to choose what you want to do.

So make sure do it with your definition of success in mind.

Because yours is the only definition of success that matters.