The best resource visualized: https://www.nobsbitcoin.com/how-does-a-lightning-replacement-cycling-attack-work/

Explained simply:

Imagine papercliping garbage to a legal bill, but then the whole thing gets thrown out because of it. So a new bill is proposed but the attacker paperclipped more garbage to it and it doesn't pass again. Eventually it is no longer possible to submit the bill and attackers win.

In this case the bill is your in flight payment that you're trying to redeem on chain before the timeout.