Many retired NFL players find their second act in coaching, sports media or small business — not working for a small tech start-up.

But former San Francisco 49ers linebacker Patrick Willis wouldn't have it any other way.

For the past few months, Willis has been working for Open Source Storage, a start-up specializing in cloud technology. He is the EVP of strategic partnerships.

"I think my proudest accomplishment is being here," Willis told CNBC.

Willis announced his retirement from the league in March 2015, ending an eight-year career at age 30. Sustaining multiple injuries contributed to his decision, but so did the desire for something new, he said.

The tough part was figuring out what came next.

"When I no longer had that passion ... to get up each day and put forth my best efforts, I just knew it was time for a change," he said.

Making the decision to retire wasn't easy, but he had to trust his gut.

"Everybody in the world had everything that they thought I should do and the way they wanted me to do it," Willis said.

The difficult decision taught him a valuable lesson about himself — and about making tough decisions.

"I have always been the kind of person to do what feels right for me, do what feels right in my heart," he said.

A chance encounter would help him find a new path.

"As I was looking at some other things, I happened to come across a guy that happened to be my neighbor, and we just had a conversation," Willis said. "One thing led to another."

That guy was Open Source Storage CEO Eren Niazi, his future boss.

The move to leave professional football might not make sense to many, but Willis said his new job is very rewarding.

"I'm grateful for those times, but I'm even more grateful for the opportunity that I have now to be working at OSS, to be a part of the tech field and to be using my brain the way I get to use it every day."

"I've just always been a different type of person, [the type] to create your own path, do things that haven't really been done," Willis said.

"You must trust what's inside of you. Trust what was put there."

Video by Jeniece Pettitt .

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