I once knew a very impressive girl. She could sing beautifully, dance phenomenally, was physically attractive, and had excellent social skills. As far as I could tell, there was only one major flaw that she had. It was that she did not believe she was any of those things (though I am sure there were other things I did not know about). Frequently, when she would sing, she would immediately say “I sounded so bad”. She would likewise critique herself on everything she did, even including her cooking (which also was quite tasty). After spending a significant amount of time with her, I realized that she was not just saying those things to sound humble to others, she truly believed that she was not good at any of them.
Being an optimist, I thought that blasting her with sincere compliments would help her. I would compliment her singing and try to tell her about her talents when she would talk about how bad she was doing in life. Surprisingly, my sincere compliments did not work, and it turned out detrimental to our friendship because she would get frustrated with me for complimenting her.