Every time the chain gets congested, I think of the mempool as a morning rush hour queue: your transaction isn't "sent and done," but rather waiting at the door to be called. While waiting, a few quite realistic things happen: First, others may pay extra to cut in line (increase the fee), pushing your transaction to the back; second, if your transaction has a dependency on a previous one, and the earlier one gets stuck, the later one can only stand still together; third, waiting too long might cause nodes to treat it as an "expired order," you think it's still pending, but many others have already lost sight of it.

Recently, during the upgrade/maintenance of a major mainstream blockchain, everyone in the group was speculating whether the ecosystem would migrate. I think there's no need to rush into imagining a migration drama; first ask yourself: do I need this transaction to be completed now, or can it wait? Frankly, during congestion, I prefer to do fewer transactions, reducing the noise from fees and failed retries, and avoid making the risk frequency too sharp.