Smittie and Lesley -- my first thought was the same as yours. I shop pretty slowly and keep things til they fall apart, unless they stop fitting (my feet keep growing ). If I did one in three out, I would run out of things to wear!
My guess is that her psychology is a little different than ours, and the 3 item policy probably has to do with preventing impulse buys (especially since she's shopping thrift stores, which are fertile grounds for impulsive decisions!). Everything she adds has to be "worth" as much as three things already in her closet.
Also, looking at her spreadsheet, she has notes about items that feel so-so or might need replacement soon. So three out may be an extra push to help her get rid of things she's hung onto for too long.
Anyway, I agree that it wouldn't be a sustainable strategy in the long run, but good for someone who feels their shopping and/or culling habits need a reset. And she's explicitly only doing it for a year. If she adds 24 items (2 per month), she'll eliminate 72, bringing her down to under 200 items total. Not a huge change, but maybe just right for her goals.
