Sacrifice. The will to sacrifice for the greater good was through line for the film.
Thanos had the will to sacrifice half of Titan to begin with. He had the will to sacrifice the daughter he loved most for the good of the universe.
Cap was unwilling to sacrifice Vision. Peter was unwilling to sacrifice Gamora. Gamora was unwilling to sacrifice Nebula. Scarlet Witch was unwilling to sacrifice Vision. Only by Thanos' unstoppable will were any of these players willing to be pushed to the same level and depth of sacrifice.
The only player who displayed any semblance of will was Dr. Strange who was willing to let Peter and Tony die to protect the Time stone. When he gained the knowledge of 14,000,605 alternate futures, the greater good was giving up the Time Stone and saving Tony, which meant sacrificing half the universe... hopefully temporarily, to save all the universe. This is, of course, conjecture on my part that this is all a part of the master plan for Dr. Strange.