From what I understand from the answers, this is not a feature of a given rating range (2200+, for example), but rather something variable determined by the player rating. That is, if I have 1600, I will consider 1800 more resilient (tough), but if I have 2200, just 2400 would be too tough.
howrever, my personal history shows that only from the 2000+ this relisience exist, have I ever either smoth lost or smoth win below 2000 rating range ... Although in recent years I have noticed a different stance on
chess.com where players of 1200 are highly competitive!
In my youth, the 1200 rating did not exist, I never had this rating as far as I can remember... My first rating was something like 1500 and I would win some more points up to 1600~1700 in FICS or playchess... Todays I see 1200 players which KNOW play chess, not total beginer with fighting to understand knight-move-rules...
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I'm talking 'resilience' in the context of fighting using the resources one have even if the position is completely lost. Bluffs, desperate attacks, avoiding exchaging pieces that would allow more chances of counterattack, etc. These players never give up unless all possible tricks are neutralized. If I play h3 (or h6) and this player bets everything on a back rank mate, he folds immediately!
But I am also associating the word 'resilience' with willpower, competitiveness, etc. I think one thing leads to another, I would say!