We all do sometimes.
When we feel disappointed by an outcome or by a situation, it is almost always because we had an expectation about it. It is almost never about the other person.

Yes, they might not have said or done what you had thought they would, or done something in a way you wanted, but that’s not on them! You were the one who created that expectation, and you are the one let down by that expectation.
So should we never have expectations??? It’s pretty hard to be human and not have them!
Instead, try to get clear about what you are expecting and why. Then communicate those clearly to others involved. They may have a different expectation of the outcome of the situation. It’s good to get clear from the beginning! And then, even if you feel you’ve done this, and you still end up feeling frustrated or disappointed by things not turning out the way you had wanted them to, ask yourself this question:
What’s the story underneath that expectation?
🤔 I feel scared I can’t handle something.
🤔 I feel alone and can’t count on anyone to be there for me.
🤔 I feel like if I’m not in control of a situation, it will end badly for me.
Whatever your story is, THAT’S what the frustration and disappointment is actually coming from. Release the other person or people from your disappointment.
Does this mean you continue to carry on in a situation that doesn’t serve you or what your underlying need is? No. You are your best advocate and you can still seek out another avenue if you still need that thing to be handled in a certain way. But continue to ask yourself why. Why do you think you need that thing or that person, or that situation to be handled in a certain way? Because you think only that certain outcome will do? It’s an opportunity to learn more about yourself and your stories, and who you are without them.