Just now I encountered mempool queuing again, watching my transaction sit there like a receipt spit out by a ticket machine... Basically, you hand over the "thing you want to do" to the network, and miners/validators then select and pack transactions into blocks based on fees and various packing preferences. During congestion, lower-fee transactions are easily left behind, and after a while, they might be replaced by new transactions with the same nonce, or you might resubmit with higher fees. On-chain data tools become quite awkward at this point; the tagging system still tells you "a whale is buying," but that transaction might also be stuck in the queue, with a significant delay, which can be quite funny. Anyway, I now first look at the pending transaction density and failure rate before deciding whether to push through aggressively.