I don't think that a lot of our stress, worry, and mental anguish comes from our reactions to external events.
Instead, I think it is our reaction to how we reacted, compared to the way we think we should have reacted.
For example, when I was younger, I used to get nervous and dread going to the doctor or dentist because I might (or would) get a shot. What I realized was that a lot of the suffering was because, almost unconsciously, I was beating myself up over being nervous - that I was being a wimp and should be calm and cool.
When I stopped beating myself up, and said "OK, you're nervous, it's just a reaction, it's temporary, and you'll be fine after the appointment. Just let yourself be nervous", I ended up much better off.