How do you know if you are working out too little or too much?

Question :

How do you know if you are working out too little or too much?

Reply :

I just go by how my body feels. Sometimes 6, sometimes 7 days a week. You should leave at least 48 hours of rest between each muscle group, though.

The more I read into things, sometimes I wonder if I’m overdoing it by doing three failure sets. When you read into Mike Mentzer and Dorian Yates, they did 1 intense set per muscle group until failure and spent 4 hours a week in the gym.