“Be pitiful, for every man is fighting a hard battle.”
I find this quote from Ian MacLaren, often misattributed to Plato, wonderfully helpful in illustrating the difference between sympathy and empathy.
Understanding that everyone is fighting a hard battle is sympathy. Discovering how they’re fighting that battle is empathy. Said battle is a useful metaphor for the sum of that person’s mental burdens, and informally auditing those burdens—simply by asking yourself, “What might this person have to worry about?”—can help you empathize with them.
The person whose mental burdens you’re auditing doesn’t even have to be real. (That probably sounds more Scientology-y, than I’d intended.) Personas, a staple of user experience design, are hypothetical representatives of groups with specific characteristics and needs, and considering what their worries may be can work just as well to build empathy.
Make the process a bit of a habit, and you might discover, for example, that the route you took to your destination would have been impossible for someone in a wheelchair to navigate. Or that a deaf person wouldn’t have heard a PA announcement on the transit system. Or that a parent with a crying baby would have had to endure impatient looks.
For this exercise to continue to bear fruit, you’ll constantly need to diversify your persona pool or risk lapsing into relating only to your own kind. In any group of people, look around to assess who isn’t there, and how they’d feel if they were there. Chances are you’ll start to see a whole lot of barriers to participation that you never realized existed.