> and that after having made it he immediately resigned
This is an absolute mistake and is a bigger reason that he won't become a GM than his age.
Most chess players should NEVER resign. Ever. I mean it.
1) Chess below grandmaster is a game of mistakes.
It's actually one of the things I hate about chess and why I don't regard it as so much of an intellectual pursuit as people think. You can be playing an amazing game and then suddenly one thing you missed will kill you.
GM Ben Feingold has a great quote (paraphrased): "The reason why you are rated 1900 is that you will play a bunch of moves, finally hang a piece and I will beat you. The reason why I am rated 2400 is that Magnus will play 80 moves that are all slightly better than mine and I will lose."
2) Your opponent has to be able to capitalize on the mistake
If you hang a piece, the opponent cannot disregard the fact that it is a trap. At 1400, it's probably a hung piece. At 1900 it has a 40/60 chance of being a trap. At 2100, it has a 60/40 chance of being a trap.
Your opponent doesn't know you made a mistake so don't tell them. Pull out your poker face and play on. I have won countless games that I should have lost because of this.
3) Playing down a piece actually makes you a stronger player
Okay, you're down a piece. Are you just going to sit there and lose? You might as well try something first. Maybe there's a positional upside, maybe the defense got weakened, etc. Sure, you're normally going to lose. However, being down a piece has a way of knocking you out of your normal play style.
4) Being unable to convert an advantage makes the opponent frustrated
The number of people who get complacent after taking a piece is quite large. Lots of people lose after being up a piece because they let down their guard. And then they lose.
And there is nothing more frustrating than being up a piece and playing someone who is mounting an excellent defense. Your instincts are screaming that you shouldn't be having to put in this much effort and you have to resist them.
5) People play computers so often that they forget that playing a human is a completely different game
People get tired. People get frustrated. People get inattentive. People want to go home already.
All of these things can lead to mistake.
Below Grandmaster, chess victories generally go the person who makes the second to last mistake. You're always the last mistake if you resign.
Never resign.