On disappointment…
“Don't feel harmed — and you haven't been.”
~ Marcus Aurelius
One of the biggest mistakes people make in this situation is thinking that the outcome "says something" about you, when in reality it's almost always due to factors that have nothing to do with you -- whether it has to do with timing, politics you're not aware of, internal considerations you're not privy to with respect to those making decisions, etc, etc.
"Zoom out" and look at the big picture -- a great big world, only a teeny bit visible to you, and a long list of conditions -- many of which are completely opaque to you -- which will determine whether it goes "your way". It either does or it doesn't. Do you best and nothing more.
Remember that following desire promises the attainment of that of which you are desirous; and aversion promises the avoiding that to which you are averse. However, he who fails to obtain the object of his desire is disappointed, and he who incurs the object of his aversion wretched. If, then, you confine your aversion to those objects only which are contrary to the natural use of your faculties, which you have in your own control, you will never incur anything to which you are averse. But if you are averse to sickness, or death, or poverty, you will be wretched. Remove aversion, then, from all things that are not in our control, and transfer it to things contrary to the nature of what is in our control. But, for the present, totally suppress desire: for, if you desire any of the things which are not in your own control, you must necessarily be disappointed; and of those which are, and which it would be laudable to desire, nothing is yet in your possession. Use only the appropriate actions of pursuit and avoidance; and even these lightly, and with gentleness and reservation.
Don't demand that things happen as you wish, but wish that they happen as they do happen, and you will go on well.
If you wish your children, and your wife, and your friends to live for ever, you are stupid; for you wish to be in control of things which you cannot, you wish for things that belong to others to be your own. So likewise, if you wish your servant to be without fault, you are a fool; for you wish vice not to be vice," but something else. But, if you wish to have your desires undisappointed, this is in your own control. Exercise, therefore, what is in your control. He is the master of every other person who is able to confer or remove whatever that person wishes either to have or to avoid. Whoever, then, would be free, let him wish nothing, let him decline nothing, which depends on others else he must necessarily be a slave.
~ Epictectus