Another good reason to lift heavy stuff is so that other stuff doesn’t feel nearly as heavy. Consider riding a bike. The strokes of the pedals are a continual flow of the combined movements knee extension and flexion mixed with hip extenension and flexion. Another movement that involves opening and closing the hip in combination is the deadlift. We can extrapolate the force of every peddle stroke is some percentage of our 1 rep max deadlift. How many times can you deadlift 50k? I am sure it is a crap ton(technical power lifting term). What about 85k, or 125k? As I am sure you know the higher your 1RM deadlift than the easier anything less than your 1RM will be to do multiple times. The link between absolute muscular strength and muscular stamina is not directly correlated but the correlation is strong. The stronger we are, the easier everything else is. Back to the bike analogy, if you increase the capacity to move your hip and knee by increasing your deadlift by a given percentage then every peddle stroke requires less effort. This construct applies to most of the functional movements we practice in the gym. Have you ever been washing dishes, or painting and had to take a break because your back was fatigued? This is nothing more than muscles being overloaded. As we get stronger and stronger and the limits on our time domains get longer and longer we increase our ability to get more done. We can never be too strong. We are going to keep trying though.