LEARNING to give as close to 100% physically as is possible without undue emotional involvement is a... LEARNING experience, for most people at least.
Just because you cant do it doesnt mean it isnt valuable, or that you cant learn to do it better.
Just as with most things, it will be hard at first, keep trying, and you will get better.
If you never plan to get anywhere near your physical limits or really push yourself, this isnt really important. But if thats not the case, the closer you get, the more advanced you get, the more important this will become.