Paul Graham • How to Write Usefully

Let's put them all together. Useful writing tells people something true and important that they didn't already know, and tells them as unequivocally as possible.

Useful writing is bold, but true.

It's also two other things: it tells people something important, and that at least some of them didn't already know.

Useful writing makes claims that are as strong as they can be made without becoming false.

I believe the formula I've given you, importance + novelty + correctness + strength, is the recipe for a good essay.