Either she's got a painful blister, the balls of her feet have had enough or she wasn't feeling very well.
And while it may be none of the above at all, it still came as a surprise to see Kim Kardashian wearing flat heels.
The likely reason was that she had a flight to catch and wanted to stay comfortable - not that that's ever stopped her wearing sky high heels on a plane before.
Is that you, Kim? Miss Kardashian broke away from her heels and big hair in flat boots and a hat as she flew out of New York yesterday
Kim, 30, also kept her long, thick wavy dark tresses hidden beneath a woolly hat, not cascading down her shoulders or - on casual days - in a sexy ponytail.
Kim was jetting out of New York - where she has been staying this weekend - and heading for Chicago.
Still looks stunning: Even in her casual attire, Kim still managed to look effortlessly chic
Kim is launching a fashion line, the Kardashian Kollection, with sisters Khloe and Kourtney, in August.
But today she was flying solo as she met with bosses to discuss the range.
Business flight: Kim was jetting to Chicago where she had a meeting with Sears to discuss her and her sister's upcoming fashion line