Stolen & edited a bit from an anti-endo who clearly doesn't think compassion deserves to be extended to those who don't fit the "perfect mold" of a system.
Empathy: The ability to feel somebody's emotions as though they are affecting you personally. As an example, somebody tells you "my hamster disappeared last night!" -> you now feel as though you've lost a pet personally or near-personally -> you feel grief and sadness just like the other person. Not everyone has empathy. It's a trait some people develop and others don't. Some have high empathy, some have low empathy (like the editor), some have none. For some, it fluctuates over time due to different circumstances! This is often not a learned skill, but more of a base aspect that some people experience, some don't, and some do in different ways than others.
Sympathy: the ability to understand and care about somebody else's struggles, even if you don't feel them yourself. So, if somebody tells you their hamster is gone -> you realize how this affects them emotionally -> you care about this person, and are upset that they are suffering. not everyone has sympathy either! it's a scale, just like empathy. Some people are more naturally inclined toward it than others. Sympathy can sometimes be a learned skill, as well; it depends on the individual.
Compassion: doing something to relieve another person's suffering or make them feel better. With the previous example, somebody tells you their hamster is gone -> you don't want them to remain upset -> you come up with ways to help them feel better, like offering comfort and distractions, or other forms of support. compassion is solely a learned trait, not something you can be born with like empathy or sympathy. anyone can learn to be compassionate, although some may struggle more with it than others; it's a skill, just like anything else. Learning to acknowledge others and treat them with compassion is part of building healthy communication, especially when it comes to neurodivergent intersectionality.
The difference between all this doesn't get through often, especially outside of low/no empathy circles. We thought the distinction was important enough to reconstruct in a safe environment.