Don’t exercise too much. You wanna take the car out to have the motor running every once in a while but if your driving 200km/h everyday the engine is going to wear out prematurely
Indeed, overtraining is bad for you in all aspects, it even hampers training progress - it’s really good for nothing. I heard that you can avoid overtraining by keeping an eye on heart rate variability - if that is low, you are either over-stressed or overstrained, and should tread lighter. Some fitness trackers can measure HRV.
One thing I've been concerned with lately is the tradeoff between systems that strengthen with training and systems that degrade with use.
Most of my favorite forms of exercise (climbing, hiking, running) are pretty hard on my joints, along with several other risks like shin splints and pulley injuries. I know there's some capacity to strengthen tendons and ligaments, but I can't find decent data on what tradeoffs I'm making at what levels of activity. Replacing everything I do with swimming and intermediate-rep weight training would almost certainly offer a better tradeoff, but I want to at least work out what price I'm paying.
Their are workouts that strengthen joints up to a point and significantly reduce injuries. The trade off is you need to specifically focus on them and their are a lot of at risk joints.
More important in many ways is knowing what pain is a sign to immediately stop, and take time off to recover from. Taking a week or two off now can prevent significant long term issues.