The capacity to understand or feel what another person is experiencing from within their frame of reference. – Wikipedia
What you have when you truly understand your users and their emotions. You can’t get it looking at data in Google Analytics. This is where qualitative research comes in; stuff like user interviews, reading feedback, etc. You are not your user; to understand them you need to talk to them and share their experience. When’s the last time you accessed a website with a screen reader? Venture outside of your own context; look at diversity of gender, age, ability, etc. Follow accessibility guidelines.
- Sympathy vs. Empathy in UX – Nielsen Norman Group