The Doctor: People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint - it’s more like a big ball of wibbly wobbly… time-y wimey… stuff.
Mark: you don’t have to study, let’s just talk.
Erica can’t.
Mark: why?
Erica: because it is exhausting. dating you is like dating a stairmaster.