Why did he resign so early???

It looks like he's losing the e4-pawn, which would be a logical reason to resign in a game between experts or masters, but maybe not 1400s. Perhaps he was frustrated with himself.

play on-the other guy night make a mistake-still early in the game

I do this from time to time. I get super frustrated at myself and even though I know I can play on, resign instead.

After I make a mistake like that, to a move I know, see coming and then ignore, my will to try to play on is gone.

It's pure saltiness, tbh lol

Perhaps he had to go somewhere.

No reason to resign.  After 10.Nd1 Nxe4  11.Qc2 Nf6 White can win back the pawn by taking on c4 either immediately with 12.Bxc4 or after playing 12.Ne3.

@Clavius I don't see how he wins back the pawn that he lost on e4 in that line. White still seems to be down a pawn, unless I am missing something.

after Nb1, white has compensation for the pawn

he probably had to go

I don't understand at all.

It's nothing to resign. He can always start another game. Why continue playing a pawn down for nothing if you don't feel like continuing on? It's not like he paid to play in a tournament or anything.

I occasional resign because I'm yielding to force majeure -- e.g. the dogs have to go out -- there's a phone call I've been waiting for -- my wife needs me to go to the supermarket to get paper-towels and yogurt right now etc. at least 50% of my resignations have nothing to to with my asessment of my current position on the chess-board

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Maybe the football or basketball or hockey game was starting.  Maybe his old lady was yelling at him to turn that shit off & get in bed.  Hmm.

I vote for the old lady yelling at him, lol

+1