SoCalRebel is right. Even the best real-life managers can out-think themselves. If a guy's red-hot, that's one thing. But with all things considered equal, go with your gut and shrug off some usual bum going 4 for 4 with 8 RBIs or whatever. You'll drive yourself crazy otherwise.
And when you have a terrible day, don't freak out. It's a long season. There's plenty of time to get back on track.