the purpose of weight training is to break down muscle and then have it recover back. you need to do both to grow muscle
the problem is people watch goofball pro's on youtube training like gorilla's and think they can do the same thing. we had one of the top pro's in the past decade on our podcast and he wants people to believe that training intense is the secret to building muscle. WRONG. the secret to building muscle is genetics PERIOD. if your genetics suck you aren't building shit no matter how intense you train sorry.