How to build a strong heart? Let yourself not blush when you meet anything.
Make more friends. You know, everyone blushes sometimes, and people have to be cheeky when they are alive. Otherwise, how dare you live? If you want to be strong inside, tell yourself that the reason for finding yourself is not that others make you blush, but that you care too much about other people's opinions. If you don't care, no one else will care. Just open your heart, accept everything and let nature take its course. When you are alone, of course, there is nothing, because everyone is the same. When you are alone and there are no others, you will not be so defensive and can do whatever you want. But when you are in front of everyone, you feel that you have gathered too many eyes at once, and you are always afraid of other people's opinions, so you can't let go. Change takes time, experience and experience.