Comment by Squeeky on Solo Leveling - Chapter 178

For everyone who is confused;
The cup of reincarnation is an item with the power of the absolute being(the one the rulers killed) they use it to revert time up to 10 years. But this only affects normal beings (meaning higher beings like the rulers and sovereign will still go back in time but they are aware of it. Where as the normal people wont notice a thing) So Sung Jin Woo decided that he needs to use the cup and turn it back 10 years to the past to meet the sovereigns in the dimensional crack to fight them in there to avoid all thr casualties(this also means that the rulers wont have to open gates on earth to make sure that earth will be supplemented with magic to withstand the because there will be no war taking place since jin woo faced them before they even could set foot to earth) 

This would also mean that jin woo will be the only person in earth with the knowledge of everything that has transpired. Hence, why the upgrader was freaking out because he was willing to sacrifice himself and not be remembered as the person who saved everyone and at the same time fight the most difficult fight that everyone on earth should have experienced alone. All so he wouldnt have to bear losing all the people that he lost.