At lower weights, it's easy to 'have good form'. The muscles can easily compensate for each other and one doesn't have to think too much about which muscles to

At lower weights, it's easy to 'have good form'. The muscles can easily compensate for each other and one doesn't have to think too much about which muscles to contract/focus on. As the weight increases, it requires more focus to ensure that you are keeping your form and positioning and even just to engage your muscles `in the right way`. Form becomes more important/a pre-requisite in a way that ramps up as the weight increases as mistakes become harder to correct on-the-fly. The tolerances decrease and so the technique becomes more important.