The only thing that is gaurenteed is that you always have to choice to do the best you can with what you have got. Some days that 100% might only be 80% of another day but as long as you can look yourself in the eyes and say hey we gave it what we had then that is just fine! You're actions, you're mind, and you're body are between you and you alone.
The above image is me today, I have been working hard. I have had a lot going on. I may not look the best I have ever looked, or be the fastest I have ever been, but I know that I have been doing the best that I can with what I got right now, and knowing that I can still be proud.