Two examples. First "switches" from past to present, second stays in past.

Emily sunk lower in her chair, strobe lights dancing across her face. I honestly felt bad for her, the one girl no one wanted to dance with. There are always those people at high school dances: the ones who are magnetically attracted to the corner, the ones who don't even bother congregating as one rejected group. They give up hope.

Emily sunk lower in her chair, strobe lights dancing across her face. I honestly felt bad for her--the one girl no one wanted to dance with. There were always those people at high school dances: the ones who were magnetically attracted to the corner, the ones who didn't even bother congregating as one rejected group. They gave up hope.

The first one sounds right to me. The second makes it sound like high school dances are a thing of past, when no, there are still dance rejects hanging out in corners at this very second.

BUT, the first one switches tense for the "life observation," which according to common writer sense is a bad thing.

In this situation, is staying in one tense still a hard and fast rule?