My only advice (though I can never take my own advice) would be, don’t beat yourself up over it. If you learned from it, if you will never ever look at yourself in the mirror facing the same disappointment, then you have grown as a person. If you know now, more than you knew then, perhaps it’s not disappointment that you feel at all. Perhaps, it’s growing pains.
“The size of your success is measured by the strength of your desire; the size of your dream; and how you handle disappointment along the way.” ~ Robert Kiyosaki. Smart fella.