I find myself reasoning thus: a little upset is not worth getting angry about. I'll save my wrath for really big upsets. However, since I am not in the habit of letting my negtive ffelinggs out, I don't even get angry when something big bothers me. The conclusion I have come to is to let my feelings out (in a safe place) about the slightest thing. That way, I'll be in the habit of expressing them also when a big upset comes along.
On another subject--When I heard that the cancer had spread from my colon, my first thought was, "I must live long enough to finish my memoirs". The second thought was, "I must clean up my life, so the people who have to handle my affairs after my death will have the minimum of messes to cope with. I found myself not only deleting emails, but also unsubscribing from good causes that do not have priority for me. I am also terminating my membership in various organizations, not only to save money, but also to have fewer things to think about.