As a puzzle constructor my aim is to make puzzles that, on average, about 50% of the people who attempt them can solve. That 50% is a mix of spatial reasoning, knowledge of or skill at finding relevant information resources, time available for the puzzle, and dumb luck. Secondarily, I like it if each of my readers is at least occasionally stumped by something that someone else can get, and also if each of them can at least occasionally answer a puzzle without having the satisfaction of it taken away by feeling that it was made deliberately trivial.
1 By obscure I mean that a distinct minority of my readers know they exist. I do not generally check my puzzles against these tools when determining whether a puzzle has an appropriate difficulty level.