When the network is congested, looking at the mempool is pretty much like watching the rush hour queue: your signed transaction is first thrown into the "waiting lounge," miners/validators don't care how carefully you've written it, they only look at who offers the higher tip and which one is easier to execute. Transactions with low gas stay stuck all the time, and sometimes they get replaced by higher-priced transactions with the same nonce; what's more awkward is that a whole string of your transactions can get stuck because of this nonce, and if your script isn't handled properly, you can lock yourself out—I’ve been there before... You can only speed it up or resend to get out of trouble.

Recently, a bunch of people are talking about modularization and the data layer, developers are excited as hell, but users are mostly confused; but for ordinary people, no matter how the chain is split and combined, your transactions still need to queue during congestion. Anyway, now I always glance at pending before placing an order, so I don’t impulsively leverage myself into a long queue.