Have you ever been listening to the radio when a song comes on that takes you back to a place or time in your life that you wouldn't have thought about if not for that song? Songs can do that. The associative properties they have are powerful.
"If You Leave Me Now" by Chicago always makes me think of the roller skating parties they'd have at the school when I was in 5th or 6th grade. For some reason, they always played that one when it was a couples skate. "Purple Rain", by Prince takes me back to high school in an instant. Then of course, there are the songs that remind me of "her." "Her" is different for each song. Sometimes the memories are wonderful, sometimes they're painful. You probably have a "her" or maybe a "him" that you think of when that special song pops up on the radio.
As a musician, I find that certain songs become difficult to perform if I've associated them with someone too strongly. I get to thinking about things other than the performance, and I mess up. Occasionally I even take them off my set list altogether for a while. Other times, doing that special song is just what I need to get me inspired.
Here's to hoping that when that one song comes on the radio, the memories it brings to mind are pleasant ones.