This is the first of a four-post series about leaving your own agency:

I'm leaving Humongo. Saying that out loud seems kind of unbelievable. I never thought I would leave the agency that I founded 15 years ago, but it was time.

A year and a half ago, I sold my agency to Source Marketing/MDC Partners, after growing it from the ground up through lots of blood, sweat and a few tears. We work with some of the most awesome clients on earth. And I've been fortunate to be surrounded by some of the most talented, brilliant and fun people in the business. Seems pretty perfect, right?

Yet I was bored. Uninspired. I've felt like the last couple of years have been more of the same, and that I was no longer living by the credo I so identify with: "Do something that scares you, every day." I craved the opportunity to do things I hadn't done before. If any of your friends were to tell you the same thing about their career, you'd tell them that it's time to move on.

But how can a founder leave an agency? It happens all the time as a result of mergers and acquisitions, where leaders cash out or get pushed out. But this was different. I was thinking about leaving the agency that I love. About leaving the coworkers that I hired, and who are like my brothers and sisters.

For me, the ultimate decision came down to a few factors. I found that I couldn't answer "yes" to all of these questions:

• Are you doing something that scares you nearly every day?

• Are you having fun every day?

• Are you proud of what you've accomplished at the end of the day?

• Are you consistently learning something new?

Having just enough "no" answers told me that it was time to leave Humongo. With that , a million things went through my head. What would my coworkers think? How would this impact our business? Can I separate my personal brand from my agency of 15 years? How would I find the right place to move to?

About a week after mentally accepting that it was time to move on, I saw Mike Germano, the president of Carrot Creative, tweet what he does at the start of many weeks: "I love Mondays." I knew at that instant that I had made the right decision to move on. More important, I knew where I had to be.

I needed to be in an organization that could support research and development (yes, that exists in the creative business). I needed to be in an agency that could see the past the title "agency" and deliver goods and services beyond what's been done before. I needed to be in a place with the passion of small, but the power of big.

Today, I start my first day at Carrot Creative, in New York. Obviously I'm biased, but you can tell everyone that I said it's the hottest agency in Brooklyn (or in all of New York for that matter). I'm now a proud member of the team, feeling energized, excited, and a little bit scared. And that feels totally awesome.

Next post: How to find an agency culture that matches your personality.