I think the biggest disappointment comes to those who expect too much or simply expect. Expecting things to be in a certain way is judging things before they happen and we, as humans seem to naturally have this ability built into us like a dog tracking scents. We survive from judging, so anyone who is adamant they don’t judge people are lying to themselves.
But, I think there’s a difference in letting things be and expecting things to go your way or run on one track.
The only way out of disappointment is to stop expecting and just do/live.