Wrong! Overactive imaginations have led to most of the world's greatest discoveries (next to plain dumb luck). The trick is to temper your imagination with reality. Certainly look at a goal and think outside of the box if necessary to achieve it, but when your ideas conflict with established fact, back up a couple of steps and approach from a different angle.
And even if you never manage to get a grasp of what you're trying to achieve, you can still channel that imagination into something like writing novels or screenplays. The guidelines there are considerably less stringent, and you might prove to be an inspiration to others. I don't believe in Asimov's 'positronic brain' any more than I believe in putting Cheeze Whiz on a pizza, but he inspired me to seek out scientific facts.
