The mind will continually throw up all kinds of thoughts, without us even trying. This is a given. Strong people know the inevitability of this, and do not allow stressful thoughts to be engaged for long. They may arise, but they are not tolerated. We see them merely like little flies buzzing around the head of a bull.
Tollerate is a strong word. I prefer the notion of allowing but not "Taking Delivery" of every thought that pops into your mind.