Is that a generic claim? I'm making a specific, counterintuitive, and empirical claim about productivity and work-style of mathematicians, having been on both sides. Even for professional mathematicians, the solution to a problem can come all at once, while one is not even actively pursuing it, which begs the question of the purpose of beating your head against the wall when doing math. For just one example amongst many, see the story of Yitang Zhang, who made his breakthrough in establishing the first finite bound on gaps between prime numbers, while out at a barbeque and having largely given up on the problem after two years of effort.