The key point is that if I want to load a webpage that needs to download 100 different files, I don't care about the order of those 100 files, I just want them

The key point is that if I want to load a webpage that needs to download 100 different files, I don't care about the order of those 100 files, I just want them all to be downloaded in order. TCP makes you specify an order which means that if one packet gets lost, you have to wait for it. QUIC lets you say "here are the 100 things I want" which means that if you lose a packet, that only stops 1 of the things so the other 99 can continue asking for more packets.