"When you are in control, you are in control. When you are not, you are not." That is the simple answer.
This is a desire which is given to us, by G-d, and I do not think that anyone would claim to understand why it has to be this way. I have seen in sforim where the author says this about himself, not knowing why that is.
However, we also have a yetzer tov. There is a constant battle going on between them. Moreover, it gets easier over time. I am under the impression that after the first 40 days or so, it is a different type of game. I hope to prove myself correct. This is true of other middos and behaviours as well.