Behind every window there is a story.
When you pass someone on the street, or people watch from afar, do you ever wonder what their story might be? A furrowed brow might suggest stress, a broken heart, the loss of a loved one --- or just maybe "where did I park my car." Writers study expressions wherever they go. That's how we form our characters. When I see someone smiling or shedding tears, I try to imagine what their story might be and I take mental notes.  How many times have I watched a couple embrace in an airport, holding on for dear life, tears welling, and put together their story in my mind?
One day while waiting  outside of the airport for my ride, I noted the woman beside me sniffling, blowing her nose quite often. This went on for some time until I asked if I could help her in some way. She said "I missed my flight."
At this point I began to wonder why missing a flight could make her cry and this is what I came up with. The wedding of a loved one, a funeral, or maybe helping someone through an illness. And that's where my mental notes began.