1Typing the seed phrase into anything with a screen. This is how "hardware wallet users" get drained — the device was never the weak point.
2Skipping the recovery drill, then discovering a mis-written word years later when the device dies.
3Sending the full balance without a test transaction. $10 of tuition beats $10,000.
4Storing seed and device in the same drawer. One burglary, one fire, one flood — both gone.
5Trusting "support" that contacts you first. Wallet companies never DM, call, or ask for your words. Ever.