I meant just to get yourself started. You have had troubles, just think of a problem you had and there will almost always be something that could be thought about differently.

Thinking people at work or school don't like you
Thinking people here or on Facebook or other Internet sites don't like you
Any rejection when you tried out for something; job interview, sports, grades, promotions, etc.
Not getting a call-back after a date or email/texting that wasn't replied to
Person you meet for the first time not liking you/being "mean" to you
Giving more than you get to friends, relatives, spouse/significant other

Thinking you cannot/will not do this assignment "right".