Regression toward the mean refers to the mathematical fact that, following an extreme random event, the next random event is likely to be less extreme (as the mean outcome is simply much more likely than an extreme outcome). Regression toward the mean was first described by Francis Galton. Galton found that offspring of tall parents were still tall but shorter, than what common sense would suggest. Basically couples that are giants tend to reproduce slightly smaller giants. Also, offspring of shorter parents were still short but also taller, than what common sense would suggest. Basically midget couples tend to reproduce slightly taller midgets.
Shortcels and uglycels can hope their physical appearance was some outlier/extreme event and that the offspring will be better looking and/or taller. Physical attractiveness in particular "only" has a heritability of 50% to 70%, so it is not unlikely the offspring will be a bit better looking.