Divide and Conquer

"Indeed in nothing is the power of the dark lord more clearly shown than in the estrangement that divides all those who still oppose him.'

Haldier, of the Lothlorien Elves
The Fellowship of the Ring

The Enemy's strategy, one of many, and arguably the best, is to divide and conquer.  If we can be sidetracked from our purpose and calling by a perceived injustice or a selfish desire, the urgency and necessity of our purpose fades, and our selfishness takes uppermost importance.  The purpose  fades, even in such cases as when it is cited as a reason for holding onto our claim of right; it becomes merely a means to an end instead of the end goal itself.