Imagine there is a aunt of mine who thinks that she is a wellwisher of mine.
I go and tell her that I am planning to start a business and she suggests me not to do that because she thinks I am incapable of doing business
I go and tell her that I am in love with a guy and she warns me not to commit. Because she thinks I cannot choose right people.
In this way, her belief always counteracts my desires and goals. She thinks she is only warning.
But any human thinks that he/she is correct. As a result, shee will keep believing that she is correct. I.e., I am dumb.
Any human actions depends on what he/she believes, but not on what he/she wants to do or says that he/she will do. Even though this aunt desires to benefit me, says that she would benefit me, all her actions will be directed in such a way that she could prove that I am dumb. Unknowingly also, she might wish to prove that I am dumb. That is what can harm me.
Enemy who has trust will harm less than friend/relative who doesn’t have trust!