Acceptance, though a hard thing to do, is an essential thing that helps you to improve in life. When you accept a friend as such with his plus and minuses, you gain friendship. When you accept a past deed, you prepare yourself to face the future, when you accept a situation, you become more comfortable. Acceptance is the essence of life and if we try to shun away from acceptance, life becomes a bed of thorns.
As K C Theisen said, acceptance is not submission; it is an acknowledgement of the facts of the situation. It also helps you to decide your future course of action. Those who accept things that cannot be changed are as wise as grass that grows in the riverbeds and those who refuse to accept are like trees there. When a storm blows, the grass accepts and survives but the tree falls to the power of the wind. Acceptance is an important character that we have to inculcate in us, to survive successfully in this world.