~snip~
For someone who does not understand the basics, even a hardware wallet will not help, because even such wallets are vulnerable when it comes to clipboard malware. It may be a sophisticated attack, but it is very likely that you have a compromised computer with a possible RAT (remote access trojan) installed.
For such a large sum, I would have definitely made a much better effort and checked everything at least ten times, but obviously everyone has their own standards when it comes to such things. The problem is that these standards sometimes come back like a boomerang and hit an inconvenient place, and then we find ourselves in a big problem.
This doesn't look like a case of some clipboard malware as the OP described that the large transfer reached his software wallet, only to find it being swiped 8 minutes later.
OK, the OP lacks to provide some very basic case details (e.g. which wallet he used), how and with what he interacted with his wallet in the past (some gross mistakes like connecting your metamask to some shady website and granting ridiculous access rights or similar stupid stuff). Who knows, too much room for speculation open.
On the other hand you're very right that much better effort to secure such amounts is mandatory. I mean the user still appears quite composed regarding such a loss, but anyway, no judgement. Even Ledger hardware crap could've prevented this very likely.
