I'm a big believer in setting yourself up for success. Thanks to many, many mistakes, I finally feel like I'm working smarter, not just harder.
Some mental mistakes I've made:
-Weekly project mindset ("new cover video every Thursday" "daily blog" ... etc.)
-Trying out for The Voice
-Comparing myself to others; feeling disappointed if my path doesn't lead me to their destinations
-Taking on too many similar gigs at once
-Setting unrealistic expectations
-Buying cheap gear for regular use (you don't have to have the best gear, but having high quality equipment which you take good care of really does make a difference)
-Buying expensive gear without purpose (what's the point of buying a car if you're not willing to learn how to drive it?)
-Feeling defeated after not hearing back from venues; 98% of the time it's not personal
When you put too much pressure on yourself, you'll start to bend. So whatever you commit to, make sure it's attainable and that you can be consistent. It's okay to have bad days or months; just get back into it as soon as you can. It will always be okay.