Remember, it is not your weakness that will get in the way of God's working through you, but your delusions of strength. His strength is made perfect in our weakness! Point to His strength by being willing to admit your weakness.
Harboring bitterness against people is actually confessing their sin to myself, over and over again. Anger is akin to confessing their sin to God, dissatisfied that he hasn't done something and placing myself in his position as judge.
. . .most people who are angry with God are angry with him for being God. They're not angry because he has failed to deliver what he promised, They're angry because he has failed to deliver what they have craved, expected or demanded.