It isn't so much rush don't hesitate as it is simply don't hesitate. The key to RTS, and to StarCraft in particular is to always be trying to gain the advantage over your opponent, no matter how trivial. Harass, if you can't harass contain, if you can't contain out macro, etc, etc, and always keep in mind that the direct path is the shortest path to defeat as often as it is to victory. All-in rushes aren't called cheese just because they end matches so fast, but because they're so binary that they're not even fun to watch. Either the rush succeeds, and the player is victorious, or it fails and they lose because of the tech and resource gap they've given in favor of the rush.
Really though, StarCraft and StarCraft 2 are just fucking hard. There are so many options open to every race in almost every situation that you pretty much have to be ready for anything.
Oh, and scout, scout, and more scout. It's all well and good to be ready for anything, but knowing is better than guessing.