Yes, we should not promise the future that we do not control.
So, why were you unable to keep your promise?
If you have come short of what you should be doing, can you make this up to him somehow? And possibly you can discover how to correct any problem, or just go back.
I was in the Navy's Hospital Corps. And I was quite impressive in classrooms during training. And I was so sure I would be so great taking care of patients.
But I was legalistic and too picky; I got even less than half my work done in a hospital.
Then I became a laboratory worker and it took me all day to do half a day's work . . . no matter how I pushed myself. Well, I am a slow reader; In my mind I read about as fast as I read out loud. So, reading lab results and looking at slides and reading blood bank tests and microbiology cultures could take me at least twice as long as other workers.
But at the time I did not realize that was a problem. Ones thought I was a goof-off and incompetent.
Some people get romantically distracted when they change a job or schedule and discover someone.
And there can be other social differences, when we make a change.
Do you know what has made a difference? I am thinking, if you have the same job but now have done it not as well . . . I would think there is something you would be able to see that is causing your performance to go down.
The social setting could be different. Your new surrounding workers might not be adapted to you, and this might affect things.