Demetrious Johnson is a former UFC and current ONE Championship Flyweight champion. However, the superbly successful MMA fighter (and BJJ brown belt) has had a rough childhood.
He was raised by his deaf mother and an abusive stepfather. Johnson never met his biological father, saying:

I’ve never seen a picture of him, not a glimpse, nothing.

One of the ways he fought back against adversity was through training, which he took seriously in high school:

When I was in high school, I spent most of my time wrestling, doing track, and cross country. Some of my friends did a lot of drugs.

When I said that I was hustling by myself… What that means is that I think when you’re in high school, you kind of like you’re still hanging out with your high school buddies, which I was. But when I took the step to do mixed martial arts, it was me and another gentleman. Nobody else.

However, his friend stopped training. But the “Mighty Mouse” persevered:

The other gentleman who did mixed martial arts with me, he dropped out. So it was just me.

So, [out of] all the people I know to this day, I did not know in high school. It was basically me going to the gym saying: “Hey, what’s up? My name is Demetrious Johnson and I love martial arts. And I love Jean-Claude Van Damme.”

In the video, his wife chimed in as well and explained how Demetrious’ mindset helped him become a good father:

I remember when we were pregnant with our first son… He goes: “I’m nervous because I don’t know what a father does.”
He doesn’t [didn’t] want to go back to working three, four jobs and not be able to put food on the table.

Johnson credits his wife for his happiness as well, saying at one point:

She is the best thing that has ever happened to me. Without her, life would be incomplete.