Tim Urban lays it out on his blog Wait But Why:

I think a great way to be a good person is to get in the habit of consciously thinking about the fact that almost every stranger, co-worker, friend, acquaintance, fling, customer service representative, driver, waiter, customer, client, neighbor, and person on the internet you come across:

• Has a family who loves them and vice versa
• Has hopes and dreams and regrets and frustrations
• Has as many thoughts going through their head at all times as you do
• Is dealing with random health problems, trying to make ends meet financially, and is probably tired
• Might be supporting one or more other human beings
• Might be just a little sad all the time about a tragedy in their past
• Might be the most important person in someone else’s life
• Is just trying to figure out how to be happy

i.e. They’re a full human just like you.

Remembering that will make you kinder and more empathetic.

— Tim Urban, Mailbag #1 on Wait But Why