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Now, think about how you reacted to that little act of kindness.
Research suggests that people who are grateful - not just by saying a quick 'thanks' but by internally processing that gratitude - get a happiness boost.
More importantly, they also tend to feel more connected to their significant other and better about their relationship overall.
A recent study by Sara Algoe, a psychologist at the University of North Carolina at Chapel Hill, found that on days when partners reported feeling more grateful for their significant other's acts of kindness, they also reported feeling more connected to that person.
In other words, what mattered wasn't how often someone in the relationship did a thoughtful thing - it was how grateful the partner reported feeling about it.
Amie Gordon, a psychologist at the University of California, Berkeley, has also studied how gratitude can affect couples. In a series of studies, she found that the more grateful couples said they were the time she first questioned them, the more likely they were to still be in that same relationship nine months later.
It's not just about saying thank you
Psychologically speaking, processing gratitude may be different than simply expressing it. So rather than simply saying 'thank you' to the person who held the door open, try focusing on how you feel about the person who did that kind act.
"My definition of gratitude," writes Gordon in a blog post for Psychology Today, "includes appreciating not just what your partner does, but who they are as a person. You're not just thankful that your partner took out the trash - you're thankful that you have a partner who is thoughtful enough to know you hate taking out the trash."
Research suggests that one of the reasons being grateful feels so good is because it helps kickstart a cycle of positive vibes. In other words, when we start being grateful, we're more likely to continue to feel positive in the minutes or months ahead.
And the people around us probably feel it too.