I've got a couple "that got away".
The first was a Blue Catfish. Mrs B and myself were fishing on Lake Wylie in April. We had caught a few bass going up a creek channel. There were people swimming ahead of us so I turned the trolling motor to cut across to the other side. While we were crossing the channel my wife had her flatside CB trolling behind the boat. Right in the middle of the channel she said "I'm hung on something". I looked, the water was 25 feet deep so I knew she wasn't snagged since her lure would run 6 feet deep at best. She done a real good job fighting the fish. She got it close to the boat once, and it ran again. The next time I thought it was ready. It was a big blue cat, too big for my net. I had my gloves on ready to pull it into the boat. I grabbed it in the mouth with my right hand. It wasn't ready. It twisted/spun and I had to let go. It got the line wrapped around my hand, and pulled the hooks loose. I blame myself for that one. I either should have let it tire some more, or grabbed it with both hands. The next week, same lake, several miles away she caught a 37 inch long Blue cat that weighed 26 pounds, 15 ounces. (on the same flatside crankbait)
The other one I lost a couple weeks later. I was fishing with my Grandsons. I hooked something big near a lay down on the main channel. I hooked it on a spinnerbait 10 feet or so from the boat. When I set the hook I saw a silver flash. (it wasn't a flathead, it could have been a blue or channel cat) It went under the boat, toward the center of the channel. It never offered to jump or come up, but didn't twist and roll like a cat does. It was strong and quick, but didn't "feel" as strong as the 50 pound flathead I'd caught a few weeks earlier. I was keeping pressure on it, getting a little line, then losing a little line for 3 or 4 minutes, then my line just went slack. It has gotten off. There wasn't any slime on my line. Catfish usually twist and roll, and they usually get slime on your line. I believe the silver flash I saw rules out a big bowfin, or gar. I suppose I could have snagged a carp somehow, but the chance of snagging a carp with a spinnerbait is slim, just like the chance of a carp hitting a spinnerbait. I wonder if it was a fairly big spot. Most of maybe all of the big Largemouths I've caught would surface, and either jump, or stick their head out and shake. This did neither. My best Largemouth of this year (7 pounds, 13 ounces) was out of the water nearly as much as it was in, after I hooked it. My biggest spot, this year (and all time) was 4 pounds, 4 ounces. It fought like a whale, but this fish was stronger. If this fish was a spot it was either an exceptionally strong one, or it would have been a new state record. It could have been a Stripped bass but they're not very common in Lake Wylie these days.