Jack Dorsey's career has had its ups and downs.
The Twitter co-founder was pushed out of his role as CEO in 2008. He then launched his credit card processing company Square in 2009, and returned as CEO of Twitter in 2015. Today, he runs both publicly traded companies.
Who you hire will determine the success of your company, he says, but, "we often obsess over the individual people that we recruit and don't spend enough time thinking about how they change the team dynamic — whether they add or detract.
"That dynamic is at the core of how a company functions. If you have a great team dynamic, it makes every single person on the team better. If you don't, it makes everything a drag."
Of course, thinking about how the individual will operate within the team is easier said than done.
"Not parting ways with the detractors quickly is a mistake I've made several times," the CEO tells Y Combinator.
"Firing someone is just really hard to do — but you have to do it sometimes — and when you understand the benefit in the outcome, it helps you get through the short-term pain."