It reminded me of this quote from Max Planck (emphasis mine):

As I began my university studies I asked my venerable teacher Philipp von Jolly for advice regarding the conditions and prospects of my chosen field of study. He described physics to me as a highly developed, nearly fully matured science, that through the crowning achievement of the discovery of the principle of conservation of energy it will arguably soon take its final stable form. It may yet keep going in one corner or another, scrutinizing or putting in order a jot here and a tittle there, but the system as a whole is secured, and theoretical physics is noticeably approaching its completion to the same degree as geometry did centuries ago. That was the view fifty years ago of a respected physicist at the time.

Basically, there isn’t much left to be discovered in physics, so don’t bother. (Good thing he didn’t follow that advice.) Then, Einstein comes along and is like… you know Newton’s “laws” of motion? I broke 'em. He also broke the aforementioned “law” of conservation of energy.

So, while we actually do understand the physics of the Big Bang until about the first few milliseconds (not much left to be discovered), we don’t know what we don’t know.