Why a lot of effort required to do sth you are aspiring for?

Why always it is a battle in oneself to do and not to do when we venture for sth that we are aspiring for? This battle of inside takes long hours to decide to go for it or not. I nearly every-time experience this when I try to go on a new mission which usually creates a kind of mind jam and thinking comes to a standstill and this havoc cause such a damage to the activity you are going to perform that it completely shatters your imagination and aspiration. When this battle will get over I don't know. But one thing I can understand by this recurring incident that many battles are lost because of it.