When doctors prescribe medicine, they provide a dosage that is going to help manage or eliminate the cause/symptoms appropriately and effectively. Too little and you’re looking at an ineffective dose and possibly longer recovery period. Too much and it may be fatal.
The same applies to exercise dosage. Too little and you won’t get the stimulus necessary to have the body adapt. Too much, and you may override the brain’s ability to keep you safe (muscle pulls, connective tissue tears, etc.).