Almost caused a crash just now: I accidentally added an extra character when copying the address, and only realized it was wrong after sending it out. Luckily, the mempool was congested and queued up, giving me a few minutes to cancel/retry... To put it simply, on-chain transactions are not "click and go," more like waiting in line to buy tickets.

When congested, your transaction first hangs in the pool, and miners/packagers will pick the "more attractive" ones to include in the block first. Lower fee transactions are left waiting, and sometimes they can be replaced by the next transaction from the same account (nonce system), so sometimes you think it hasn't gone through, but it's just stuck at the end of the line. During airdrop season, this is even more obvious—task platforms with anti-snipe measures and points systems cause everyone to interact wildly like clocking in at work, and the mempool gets directly flooded.

Now I basically don't compete for those few minutes; I prefer to wait a bit longer, first confirm the address and amount, then check the congestion, so I don't let emotions pay my tuition. Anyway, taking it slow is also a kind of hedging.