The trip has to be worth the gas.

In a novel, the point of suspense is to make you read the next page. It's an almost trivial step to get to, almost automatic, but I still have to want to keep reading. I do (for most competently-written novels), because the payoff appears worth the effort.

"I'll tell you tomorrow"? That only works if you're promising me something worth the wait, and if I believe that you will deliver. Almost everyone who uses this technique fails the second point. And the more you use this technique, the less I believe you. You're willing to waste my time today; you'll probably be willing to waste it tomorrow, too. So I won't be back.