If we do not have expectations, we will not have disappointments. Simple.

We have a strong tendency to want other people to behave the way we want
them to - even though, often, we are are not managing to behave that way
ourselves.
We want their behaviour to match (and thus not upset) the way our minds
have been conditioned. And that’s all it is - conditioning.

People, us, are the way we are.
Combination of genes, conditioning, ignorance, pride - and courage.

I enjoy most birds. I enjoy most cats. I don’t enjoy cats killing birds.
And no judgement.

That’s the way cats are. Very, very occasionally, we see photos of cats
who are friends with birds. Lovely - and exceptional.

Same with people - if you don’t have expectations, occasionally you will
be delightfully surprised.

Check this out. The last time you 'made a mistake’ - on what level was
that a choice.
Did you make the mistake on purpose?
See what I mean - most of the time we are doing the best we can - with the
awareness and circumstances of the time. It is afterwards the mind thinks
it could have done better.

How about experimenting - with taking it a bit more easy with yourself.
Treat yourself like you would like to treat the person you love most in
your life.