When Things Go Wrong
Today is the best testament to the fact that even though you may do everything in power to make things right, there will always be something outside of your control that will make everything go wrong.
Then, yes, obviously, being disappointed is valid. Because you gave your everything to the task in hand, you visualized what would you do when you achieved your goals and then the results which are presented in front of you, after the deduction of technicalities in the situation and circumstances, are just not what you expected them to be.
In such moments, the most important thing is the fact that you tried and believed in yourself with every ounce of hope. That belief matters. That hope matters. That effort doesn't go to waste even though it didn't work out the way you wanted. It's a lesson you have to learn, accept and remember the next time you do the same task again. But, then, when you do it, do better. Add the experience of this effort then to strengthen your belief. But, also remember that whenever you'll try, be it for the first time or ten thousandth, there will be millions of external factors which would impact your actions. Some of them are controllable, some of them will be not. So, rather than focusing on what cannot be controlled, focus on what can be and give it your best. Rest, will be taken care of by that supreme force which we can't control but which controls us all.