Where did it come from? Well, I was curious how Bitcoin worked, so I set up a little mining rig and let it run at night on my work computer. So, other than my time, which I think I did on work's time, and the power, which I think I used work's power... I saw it as a free cup of coffee.
Honestly, I was just so happy to find a booth at a convention that actually took Bitcoin that I didn't mind the crappy exchange rate.
But anyway, I don't think regret is a particularly useful thing to hold onto. You can regret things you did, and you can regret things you didn't do. Either way, there's nothing you can do about it. It feels like baggage. Hold on to too much of it and you sink. You have to find a way to rise above it and keep moving forward. If you don't, you'll drown.
I say that as someone who learned this lesson the hard way.
I spent 3+ years in a legal battle with an insurance company and their contractor that ultimately cost me more than $500,000. I was right. Period. I had been wronged. Period. The contractor and insurance company both lied and I had ample documentation of them doing so, and doing shoddy work. What I was asking for was completely reasonable. But who cares? That's not how the courts or the legal system work.
What I learned from the process was that most people just get screwed over when they go up against big companies. And it's not even close. I'd guess something like 75% of people who get into a fight with an insurance company end up losing -- and it's probably higher than that if you factor in the people who simply give up. Eventually, you have to decide whether continuing to fight is worth what it's costing you.
There will always be another "I almost caught the fish!" story to tell. Life is long. Learn from the mistakes, let go of the things you can't change, and do your best to keep moving forward.
Some situations just suck. Best not to think about it them too much.