From I Shall Wear Midnight by Terry Pratchett

     "I make it my business. I’m a witch. It’s what we do. When it’s nobody else’s business, it’s my business," Tiffany said quickly.
     "Yes, but we all thought it was going to be about whizzing around on brooms and suchlike, not cutting old ladies' toenails for them."
     "But people don’t understand what’s needed," said Tiffany. "It’s not that they are bad; it’s just that they don’t think. Take old Mrs. Stocking, who’s got nothing in the world except her cat and a whole lot of arthritis. People were getting her a bite to eat often enough, that is true, but no one was noticing that her toenails were so long they were tangling up inside her boots and so she’d not been able to take them off for a year! People around here are okay when it comes to food and the occasional bunch of flowers, but they are not around when things get a little on the messy side. Witches notice these things. Oh, there’s a certain amount of whizzing about, that’s true enough, but mostly it’s only to get quickly to somewhere there is a mess."
     Her father shook his head. "And you like doing this?"
     "Yes."
     "Why?"
     Tiffany had to think about this, her father’s eyes never leaving her face. "Well, Dad, you know how Granny Aching always used to say, 'Feed them as is hungry, clothe them as is naked, and speak up for them as has no voices'? Well, I reckon there is room in there for 'Grasp for them as can’t bend, reach for them as can’t stretch, wipe for them as can’t twist,' don’t you? And because sometimes you get a good day, that makes up for all the bad days and, just for a moment, you hear the world turning," said Tiffany. "I can’t put it any other way."