How does Harry have so much compassion and kindness?

After reading books, one thing that stood out most to me and makes Harry unique was how he is kind and compassionate beyond measure in absolutely dreadful situations. He was kind in general, Ron and Hermione were too upto some extent but Harry shows it in times of absolute despair. One example being going back to fetch Malfoy in room of requirements when they were trying to kill him in the first place. Similarly using Expelliarmus in duels with Voldemort himself.

Only exception being using Sectumsempra in hbp on Malfoy.

It feels unrealistic to an extent and at the same time so inspiring to see a person overcoming his insecurities at the time of facing death and showing the same compassion to his enemies.