Sorry you are feeling this way... (((hugs))) perhaps a visit to the CBT list of cognitive distortions would help you release some of that anger at yourself? Are you angry over things you "should" be able to do or change...? Are you sure it isn't part of life? Do you hold unrealistic expectations of accomplishments just short of (and including) perfection? NOT realistic.

Why be angry? If it's for something that you can NOW do something about, then harness that energy and write the letter or... whatever. But reevaluate if ANGER is the right emotion... acceptance of shortcomings of being human... or of other's ....

hope this helps some