At certain times in our lives we find ourselves having trouble moving on, getting over or forgiving. Each of these three problems require a level of acceptance, in order to move forward in our lives.
When we have trouble accepting something; it is because things are not how we want them to be.
Our ego, our driving force, is enraged.
Enraged, because we want things a certain way. Any other way, simply won't do. It's almost like a small child within you shouting "NO!", and whilst you don't normally physically act like a child and stamp your feet. When you have trouble accepting something you still get angry inside.
It is important that you understand that it is your 'life blood' or 'driving force' or 'Ego', that is struggling with accepting, those things which you know you have to accept.
Accepting, is quite simply calming your Ego.
Further reading at : http://www.inner-truth.net/emotions/acceptance.html