Grading examinations. I made very proper and careful preparations and of course trained hard for six months for the examination event: I paid the license, fee, membership, corrected stances, techniques etc... Only one thing was missing and that was a partner for kumite and self-defense parts. I tried to find a partner, but I failed to find one that could come to assist me in the examination. I was so frustrated: I waited six months for this moment, and my instructors didn't let me do the test because nobody became my sparring partner and they didn't offer any help. This had happened TWICE.
But, I can react to this with wisdom and philosophical calmness: it is just a belt, nothing more or less. The most important is that YOU know your own level and limits. And whatever happens, it happens. Sometimes you can't control everything in this world.