A Texas man didn’t realize how much his kind gesture meant until the recipient's family paid him back for it -- literally.

Kasey Simmons, a 32-year-old server at Applebee's, never misses an opportunity to try to improve someone else's mood.

"It's selfish really," he told WFAA. "When people smile, I feel better. It lightens my world."

While at the grocery store on Aug. 15, Simmons noticed a fellow shopper who appeared to be unhappy. Given his generous nature, he walked up to her and offered to pay for her things.

"I insisted," Simmons said. "It was only $17, but it's not about the money -- it's about showing someone you care."

The next day, while he was working a shift at Applebee's, a small party sat down at one of his tables, ordered a flavored water, and asked for the check. Simmons had no idea what was coming next.

"They ordered the cheapest thing on the menu of flavored water -- it was $0.37," he said. "But my tip was about 50,000 percent."

The woman who had ordered the water left Simmons a $500 tip. On a napkin, she wrote a short note explaining that the woman Simmons approached at the grocery store the day before was her mother, who had been lamenting the third anniversary of her husband's death.

"On one of the most depressing days of the year … you made my mother's day wonderful," she wrote, according to the Idaho Statesman. "She has been smiling since you did what you did."

"You are one of a kind," she added. "Have fun with this …. You made her year."

Simmons is grateful to the woman, and said he would like to meet her and her mother to thank them in person.