I worked at a popular pizza chain for high school and got maybe $10 in tips my entire time there. My pregnant coworker meanwhile averaged an extra $50 or more a night. Given that I was paid minimum wage at the time ($4.25 IIRC), that extra $50 in tips was a significant boost to her income.

Now on one hand I think it's fair that a pregnant woman needs more money than a high school kid who's saving up for extra toys (a DSLR in my case), so I'm not complaining about my pay. But then again literally no customer actually knew that; for all they knew I was supporting my poor family with extra income. The arbitrariness is troubling. If tips are a significant chunk of your pay, then you're dependent on either customers feeling bad for you, or generally liking you in order to make a good wage. And heaven help you if you're in a demographic group that's disliked for whatever reason.