Luckily, I haven't really fucked up yet. But I remember my first buy was in Ethereum, and I bought it to gamble (I thought it was investing 😂) with even more low-quality coins like Tron, OMG, and other coins I've already forgotten. I thought Bitcoin was outdated, slow, and whatnot.
It took several months to understand that Bitcoin should be part of a crypto portfolio. Luckily, I realized some time ago that I was wrong. There is no portfolio. It's only Bitcoin.
Not really a fuck-up, but I could have some more sats today if I had never bought any altcoins.