My flimsy defence is I was 11/12 when I got my first pigs but oh boy, here goes..*takes a deep breath!*
-I didn't think to double check the genders of my first 2 pigs
-Said 2 pigs then produced 3 babies which luckily I managed to sex properly but for some unknown reason I still took the stores word that the second piggy was female so I waited for him to give birth while left with the adult and 3 female babies...
-By the time I realised my error mummy pig and 1 baby were pregnant.
-I misinterpreted dominance behaviours which were complicated/confused by pregnancy and nursing and separated them all into single cages for a little while until everything settled down and I had a go at bonding them all again (minus Fudge who I now knew to be male)
-I thought a 100cm cage was big enough as a permanent home
-I fed a cheap muesli food
-I put 3 boars together and it ended exactly as you would imagine
-Not sure if this one counts but I went to a show and saw what I thought was a piggy with mites, this beautiful piggy was my second satin pig Honey who had hair missing on her back, older and wiser I know this was the first sign of her osteodystrophy but in my ignorance I figured I would buy her and make her mites better and get a cheap, pretty pig, wrong! I paid for regular, expensive dental treatments until we lost her to the repeated aneasthetics.
-I regularly gave them unhealthy and unsafe treats from pet stores like the dried corn, salt and mineral licks, those weird puffy donut things they used to do, seed sticks etc.
That's probably not even everything

but that's what I remember off the top of my head.