Well, I guess it wasn't a blunder, really. I just remember thinking he shouldn't have been beaten with that shot when I first saw the goal, but I was 10 and impressionable, so maybe if I saw it again today I wouldn't think the same thing.
Pay attention at the back there. In today's lesson I'd like to point out that "in fact" is two words. Are you chewing? Of the three famous Seaman blunders (not counting the ponytail) I'd contest that only one, the Ronaldinho one, was a blunder (for being badly positioned). The Nayim one I'd agree with mobile that keepers do come off their line when the ball is a long way out and I'm amazed more players don't try the long lob. I'd also bet 99% of goalkeepers would be in exactly the same position in the same situation. The Macedonia one - everyone says bad error, but what exacty did he do wrong? His positioning was fine. He jumped at the right time. He didn't fumble anything. The problem there was that he's past it and couldn't jump high enough. I don't think a physical limitation can be classed as a howler, however embarrassing it is. For that goal the true blame lies with Batty who was at the back post and ducked rather than head the ball away. Actually best howler has to go to the keeper, I think in an Irish league match, that was once used as part of an advert in then UK. Essentially the fuzzy footage shows a keeper with ball in hard winding up to throw it cricket style upfield. Sadly he get his bearings wrong or something and spins too far, throwing it straight into his own net. I'm sure (I'd have to find it on the original Danny Baker Own goals & gaffs tape) that you can see the keeper, as keepers do, start to blame his defence in anger, then think better of it.
After reading this entire thread I don't think anything can compare as a bad mistake to the Faked Flare Falling Fiasco during the Chile v. Brazil WC qualifier. The price of that error was far greater than a goal scored could ever be. Perhaps only a real boner (howler for our English fans) in the WC final could compare.