[seri]

Although I like the grandparent's anecdote and up-voted him, I would have made the same argument as you did against his point. It's just confusing and therefore unsatisfactory to use usefulness as a tool to decide how to spend your life.

The reason why one shouldn't be That Guy is not because spending all your life playing Poker, or doing Maths, or playing Chess (as in the case of Bobby Fischer) just for the sake of it doesn't benefit others, but because when your level of obsession reaches a certain point, the point of diminishing returns, you just get confused -- you can't tell whether you are still getting pleasure doing it anymore. You've been off-balanced with other parts of life for too long that you've lost the ability to approach your passion purely from intellectual curiosity, as you used to.

So the bottom line is, solving intelligent puzzles is fun, as long as you don't abuse it.