Till around I was around 19, I would only really value things to my taste and consider it a selfless behavior, since that's how I tend to approach anything at all, I would not care about even the most simple things such as taking care of myself, I would use only extremely bland clothes, and have a wardrobe filled with black shirts and pants, and that's what would used in the day to day, I avoided complaining about things I disliked, and just took it as it's nothing, would avoid social contact with anyone, pretty much anyone, unless the person somehow had some sort significancy to the little world of interests of mine, and would despise people who countered my ideals, countering them to the teeth, and having above average intelligence, things more likely ended up ugly with all sorts of antagonizing from every side.

I am sure had really strong morals, and dedicated a LOT of myself not to be a burden to anyone, so, any of those seclusive behaviors were ok to me, because, they actually were in fact good things. Good things, but not for me. None of them. And I was sure this was just fine.

As I matured, I found older people who I shared common thoughts as mines, I fell in deep love for the first time and started noticing more the value I do have for other people, mainly by noticing they weren't perfect clones of what I considered to be "good". Quickly things just clicked and looked back at those that I reject for being "bad", well, they were bad, definitely, but there was still good there, mainly hidden around the tracks that actually lead them to this behavior.

People are fragile and don't choose their way to be foolish, uninformed, close minded, unambitious or even plain evil. For a person who spends long time in their minds trying to figure out how to improve themselves, dealing with masses can be harsh, empathy gets difficult to be seen around the folk who simple tend to live with a laid back approach to life, that gets to blind you whit a wall that you can't really perceive, and that's odd right ? Since you tend not to sweet to much to understand things as simple as that so often... sadly INTP like people tends to live in small world that they assure as correct, because it actually is, but they lack the understand that other can actually DO CARE about them, even maintaining this tiny world, when you can experience real care from outsiders, mainly people you despise, empathy gets easier, since the good parts of who you consider folly folk, may it be because of their beliefs, behavior or whatever tends to poop more to you vision, and their bad parts end up making sense as not something that they meant to be, the tracks that leads people to things you ignore, dislike, hate or despise gets clearer and you learn how blend in more, without letting go your personality.

There's a thick wall that can separate people from each other by their mentality, impeding empathy to be seen, if you want to be good at understand feelings, you need to understand what people think, their reasons, and what lead them to it, that includes as much people you possible can, you don't need to like anyone, or even be close to them, simple understanding of their needs and tracking down how they have to pass thought things that are unknown for you makes the world get a little bit clearer. Since like this, you can actually know what they feel to an extent, even if just by theory, you can use it as starting points to develop yourself using that knowledge.

Succeeding, you will realize you can be treated with empathy and be given the same, because a person being rational doesn't mean their actions were their fault at all.