How do you bounce back from letting down your biggest mentor/rolemodel.

Should you just give up and live the rest of your life wondering what you shoulda/coulda done different. Or should you use it as fuel and let it motivate you to go harder then you ever went and to go above and beyond that they actually become proud of you for not letting up, thru all the daily struggles of this thing called life ? This has been is eating me alive literally and left me in Stuck-mode. Especially when you know you can do so much but the brain won't let you break out of this…

How do you bounce back from letting down your biggest mentor/rolemodel.