Wanting to be a little pessimistic before I bet the family farm on more ETH

Hi all, I have a decent ETH holding and my average cost is around $950. I am ready to put more money in even at these ATH prices because it seems as though ETH's rise and dominance is inevitable. My only question is this, tell me why it wouldn't work? Tell me why it would be a bad idea to buy more at these prices. The only thing I could think of is if Cardano and polkadot go balls out and steal a huge market share from ETH but I don't really see that happening this year. Be pessimistic for me please! its a fun investment exercise :), thanks!