The surprising reason first ladies can't wear clothes off the rack, according to Laura Bush's former chief of staff

• Anita McBride served as first lady Laura Bush's chief of staff from 2005 to 2009.
• She says first ladies usually wear custom outfits to avoid accidentally matching other guests.

First ladies occasionally wear clothes from affordable fashion brands like J. Crew, Gap, and Target for everyday events. But for larger, high-profile gatherings, they usually work with designers to create custom gowns.

This isn't just an aesthetic choice. Anita McBride, who served as first lady Laura Bush's chief of staff from 2005 to 2009, told Insider that there's also a strategic reason why first ladies don't shop off the rack: to avoid wearing the same outfit as other guests.

McBride learned this firsthand in 2006 at a White House reception before the Kennedy Center Honors.

"Mrs. Bush had this beautiful Oscar de la Renta dress, but it was one that was off the rack, not made special for her," she said. "It was a beautiful, red, elegant gown that she was intending to wear for the Kennedy Center Honors, for the reception at the White House, and then over to the performance."

As the president and first lady began greeting guests, it became clear that the Oscar de la Renta dress had been a popular choice.

"They're doing the receiving line, and at least two, maybe three other women came through the line in the same dress that Oscar had sold that year," McBride said.

Bush quickly went upstairs to change between the White House reception and the Kennedy Center Honors, attending the gala in a black lace dress instead.

"She was more concerned for these other women that had come through the line and didn't want them to be embarrassed in a public way," McBride said.

Showing up to an event wearing the exact same outfit as another attendee is largely regarded as an embarrassing fashion faux pas. Indeed, the incident made headlines, like "Laura Bush Among Four Ladies In Red."

McBride says that by wearing dresses that are created especially for them, first ladies ensure that they won't need to worry about accidentally matching anyone else.

"It underscores that it's hard, when you're in that public of an event, to really buy what other people are buying — particularly in an event like that, that is so visible and televised," she said. "So you can understand why they have to have things done just for them, particularly for state dinners or Kennedy Center Honors or things overseas. You can understand the need for the outfit to be unique."