One of the biggest causes of anger is disappointment over not getting what we expect. We expect life to work out in our favor–we want to be loved and appreciated and all that. But the truth is we’ll never get everything we want or expect. If we can accept that fact, it will do a lot to minimize our big disappointments. Disappointment is often the salt of life. 
John Calvin understood it when he expressed that we should “…let us not cease to do the utmost that we may incessantly go forward in the way of the Lord; and let us not despair because of the smallness of our accomplishments.”
Life often comes in horrible waves of despair and disappointment. But behind those realities is also the goal of discipline, with the purpose of character and holiness:
“And you have forgotten that word of encouragement that addresses you as sons: “My son, do not make light of the Lord’s discipline, and do not lose heart when he rebukes you, because the Lord disciplines those he loves, and he punishes everyone he accepts as a son.” Endure hardship as discipline; God is treating you as sons. For what son is not disciplined by his father? If you are not disciplined (and everyone undergoes discipline), then you are illegitimate children and not true sons. Moreover, we have all had human fathers who disciplined us and we respected them for it. How much more should we submit to the Father of our spirits and live! Our fathers disciplined us for a little while as they thought best; but God disciplines us for our good, that we may share in his holiness. No discipline seems pleasant at the time, but painful. Later on, however, it produces a harvest of righteousness and peace for those who have been trained by it.”(Hebrews 12:5-11).
Robert Hamilton understood this eternal concept and expressed it well:
“I walked a mile with Pleasure, She chattered all the way,
And left me none the wiser, For all she had to say.
“I walked a mile with Sorrow, And not a word said she.
But oh, the things I learned from her, When Sorrow walked with me.”
 Theodore Parker, Instant Quotation Dictionary, p. 97.