Brothers who cofounded a $100 million company say this question their mom asked every night at dinner is what inspired their business

The two Jacobs brothers first sold their T-shirts on the street. Here they are at the South Boston parade in 1993.

Bert and John Jacobs, the brothers who cofounded the $100 million Life is Good T-shirt company, grew up the youngest of six children in a lower middle class family in Boston.

When the brothers were in elementary school, their parents were in a near-death car accident from which their mother managed to escape with just a few broken bones — but their father lost the use of his right hand.

The stress and frustration from his physical therapy caused him to develop a harsh temper, they explain in their new book, "Life is Good.

"He did a lot of yelling when we were in grade school," John told Business Insider. And life certainly wasn't perfect.

"There were often difficult things happening around the house," the brothers write. But their mom, Joan, still believed life was good. So, every night as the family sat around the dinner table, she would ask her six kids to tell her something good that happened that day.

"As simple as mom's words were, they changed the energy in the room," the brothers write. "Before we knew it, we were all riffing on the best, funniest, or most bizarre part of our day."

John says this daily exercise prevented them from developing a victim's mentality of "Oh, you wouldn't believe this horrible thing that happened to me today." Instead of griping about a teacher or homework assignment, he says they would be laughing about a silly haircut a classmate got that day, or a neat project they worked on at school.

"That optimism was something that our family always had, even when we had little else," they write.

Growing up with a mother like theirs — one who sang in the kitchen, told animated stories, and acted out children's books for them, no matter what bad situation they were going through — taught them an important lesson: Being happy isn't dependent on your circumstances. "She showed us that optimism is a courageous choice you can make every day, especially in the face of adversity."

They say her unwavering positive outlook on life is what inspired Life is Good — their $100 million company that's mission is to spread the power of optimism, with the tagline, "Life is not perfect. Life is not easy. Life is good."

Since their mother's daily question served them so well in life, John says he and his brother now ask their employees the same thing when they all come together — "tell me something good" — and the results have been positive. "It leads to ideas, which lead to progress, which leads to building on successes, instead of dwelling on challenges," he explains.

By Natalie Walters