Not what I expect
There is nothing more frustrating than expecting one thing but receiving something else. You have probably experienced it with a food order where the ads looked so delicious, but the meal tasted like the paper the advert was printed on. Or, in this day of online shopping, you may have received substandard items which looked nothing like what was promised on the tin.
The reality is we cannot blame our expectations on someone or something else. The onus is on us to do enough investigation to ensure that the investment of our expectation will yield a reasonable outcome. Whether we invest it in a relationship, a job, in anticipation of a meal or an event, we must do our due diligence to understand if those things can actually deliver on thier promise.
If people have disappointed you in the past, could it be that you had expectations of them which were unfounded? It may be worth having conversations with people around your expectations of them, and then reaching an understanding with them for the sake of that relationship. We should become better at managing the valuable energy of our expectations.