Here's how it works. Ella was sad that Eric was leaving. As she watched him go, she began to cry. The two sentences aren't awful, but the writer hides—that is, readers get no emotional tug.
Here is a showing of the same scene where readers can identify:
Ella waved goodbye from the bedroom window. The first tears slid gracefully down her cheek.
That's not much, but it's enough to make readers care.
Some writers go too far and present a heavy, over-the-top picture, like the following: Tears streamed down Ella's face, nearly blinding her. For nine hours and twenty minutes she had wailed over his leaving her for another woman, but no peace came to her. She clutched his door key to her breast and caressed it as her piteous sobs echoed through the empty house.
"You don’t write about the horrors of war. No. You write about a kid’s burnt socks lying in the road."—Richard Price.