I remember being in 5th or 6th grade and seeing lights flashing across my bedroom's venetian blinds in the middle of the night. I was on the second floor of our house and thus thought UFOs were flying by. I even told my dad, who either gave me the benefit of the doubt or humored me.
I'd jump up in the night and run to the window to see what it was, but it'd be gone too quickly to see.
Finally one night, I figured it out. It was the light from a f'ing car that was passing on the highway (which was ~2 miles away from our house -- we lived in the absolute boonies). The light was diffused through trees and spread out, which is what actually confused me.
Now that I think about it, I remember being pretty convinced that there were tons of UFOs around when I was a kid...