A couple of incidents that have happened at karate clubs I've been to in the past...
When I took my 1st dan test (in 1989) there was a 4th kyu student who was going for his 3rd kyu (brown belt). He failed the test, and when he heard the result he stormed out of the dojo, got dressed and left the building.
At another club, a few years ago, the sensei came up with a kicking exercise. One of the students, a 1st dan, turned his back and walked off. The sensei asked why he was leaving the exercise and the student answered, "just because!" It was left at that, though he later said that he had a bad knee.
It's been years and years since I went to a club that recited the dojo kun but I thought about it again after recalling these incidents recently, particularly the precept "to foster the spirit of effort".
It's fashionable these days to deride the idea that karate can improve the character of the karateka, but my own experience is contrary to that. In my early karate years, we were taught that you always tried your best in karate, even if you knew you were terrible at something, or you were told to do something you hated. The feeling in the dojo was to put 110% effort into everything. You face these things head-on and accept the challenge. You try, you foster the spirit of effort. We were always reminded of this aspect of training by reciting the dojo kun in every lesson. Training this way caused this attitude to spill over into other areas of my life, a tangible effect of karate improving my wider attitude and outlook.
The 4th kyu who failed his brown belt, apart from the awful disrespect he showed the visiting 5th dan who oversaw the test, failed himself by not facing the challenge of getting back up, dusting himself off, and redoubling his efforts to try again next time. That is what karate is about. He may have failed his grading, but if you have the right attitude to 'failure' you can often get more from it than from success.
The 1st dan's attitude went against the idea of the dojo kun. It wasn't karate. It would at least be better to bow out and say you had an injury, (another precept: karate begins and ends with courtesy) and better still to do the exercise to the best of your ability - even if that meant changing the kick, or asking if you could do a hand strike instead. And a 1st dan should know that and set such a good example to the lower grades present.
Of course no one can make you do these things, and no one should. Karate is for yourself, and to strive to always do your best can reap great rewards - it's worth doing. This is one of the best lessons that karate teaches, and the dojo kun can help to keep such lessons in the forefront of your mind as you train.