When I first read this I thought, do you mean just today or ever
I've started trying to say "I'm brilliant" instead of "How could I be so stupid?" in an effort at positive thinking since my answer to the question is always, "How am I still surprised by how stupid I can be." 
Perhaps the thing with the most long-term consequences was assuring my cousin I'd look after her cats if anything happened to her. She was younger than me so I was sure she'd outlive me. That's how I ended up with 8 cats in a small apartment. Loved each and every one of them but they all liked lots of attention and I was working long hours (before my company went work-from-home).
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