First of all, from nature.
Although we can't verify the truth of reincarnation theory and the influence of genetic factors, countless examples show that human nature is different and there are great differences. We find that some people show kindness when they are very young, show natural care and love for weak things, and show infinite sadness when they realize that some unfortunate things have happened. This is a natural sympathy.
Second, from similar experiences.
If someone has suffered some kind of pain, injury and misfortune and feels deeply, then when facing the pain, injury and misfortune of others, it will arouse their own memories and produce personal feelings. In this case, they will show special concern for the unfortunate people, and at the same time they will be more likely to help in some ways than the average person.
Third, it comes from relevant education.
It can be said that from a very young age, we have been receiving education similar to "old people and old people, young people and young people". After going to school, we received the education of "one side is in trouble and all sides support". The essence of such things is to ask us to sympathize with the weak and unfortunate, and to help and support the weak and unfortunate selflessly. Through such rational education, compassion has been sublimated.
Compassion and empathy are normal and healthy emotions of a person. For an individual, having compassion will bring him closer to others and strengthen his friendship. For the society, if everyone has compassion, the society will be warmer and more harmonious.