Mankind's history, has been both a personal, and cultural exercise in finding limits. Too often we have not found the limit to something, until it has been passed. Some limits we will continue to stretch. Some after looking at history's example, have been clearly defined. Others are yet to be found and their nature uncertain. There will always be limits to test for the sake of progress and adaptation. We must learn not to keep testing limits we have already established. Or we will keep failing the tests.
However limits can be particularly subjective.