Missions often fail when you spend a lot of time building and defending your base and not attacking the enemy, trying to destroy their base.

(on KKND2)

The name of the game is crush, kill, and destroy, so it makes sense that if you don't do those things, you've failed it's goal (:

Maybe that's just another joke of the game - a prank, in this case. I think it's actually good, because it forces you to have timing, and attack even if you think you're not ready. Often the best way on a level is to attack right when the game starts (on the first levels of each campaign), when the enemy has a small defense, and you've been given more units to defend yourself. Advancing in the game, it'll take more time, but usually a more concise early army (after you've played and studied the level one time) is much better than a monstruous late one.

I tend to take a sweet long time building the base, especially in this game, 'cause it's kind of unbalanced. So to me it's a good thing....

This solved the problem to me, I hope it does to you guys too! (: