How to Quantify the Load in an Exercise

I think it's much better if we start changing our mindsets for this. How can I optimize how I deal with my athlete? If exercises are important, how can I really improve to do something more individualized but keeping the same principle for everyone? So that's why it's impossible to say eight repetitions is better than 12 or worse than four. But looking at the quality of the exercises is giving you the key. It's stupid to tell someone to do 12 repetitions after the seventh one. He'll totally lost the motor control because otherwise you are probably doing something you didn't want to do or the same. At the end we need something that is practical. Practical will