Edmar Mednis stated that in KNN vs K endgame, the inability to force checkmate is one of 'the great injustices of chess'. This seems to be defined as a drawn/drawish endgame position but where 1 side is up at least 4 points in material.
The phrase 'one of' seems to indicate there are other injustices in his mind. So, what are other 'great injustices of chess'?