One of my many, many personality quirks is my obsession with fairness. Think the first episode of 30 Rock when Liz Lemon buys all the hot dogs to spite the guy who cut in line.
I inherited this trait from my dad, who is currently engaged in his own Quixotic battle. Pops is a retired dentist/chiropractor/optometrist/acupuncturist who on occasion fills in for a friend so said friend can have time off.
About a month ago, he had a patient who left without paying. No problem, things happen. He had the patient's name, contact information and place of employment, so he called the lady and let her know there had been a mistake.
She informed him that since no one had made her pay at the time of her appointment, she wasn't going to pony up now. A sort of losers-weepers attitude toward medical care.
Too bad she didn't know she was dealing with someone with an overdeveloped sense of justice.
Sure, it may only be $75. But totally worth the sense of vindication to sue for it.