#1: Your muscles need time to recover
The biggest mistake in amateur bodybuilding is not giving your muscles sufficient rest to recover and regrow. If your muscles are aching, it is a signal to train something else while those muscles recover!
That leads to you breaking down too much muscle with never building any…

#2: It increases your stress levels immensely
Overtraining leads to a serious spike in cortisol levels which is a one way ticket to premature aging and lowered quality of life. Nobody wants that…
It has also been proven that cortisol has a catabolic effect which leads to muscle atrophy(wasting).

#3: It could lead to a serious calorie deficit
The second biggest mistake when it comes to bodybuilding is Nutrition. Not just the quality of the calories but the quantity. Exercising too much can leave you with you eating too little in a day to meet muscle maintenance requirements(in a deficit). This leads to one thing: Muscle wasting! How terrible!

So what can I do to prevent overtraining?
1) Listen to your body
2) If sore, take a rest day or exercise different muscles
3) If training heavily, make sure to eat enough and stay hydrated