For all the focus-testing and customer research that happens, sometimes a good idea comes from one person. That was the case for the new Ford Bronco’s storable doors.

Like the Jeep Wrangler, the Bronco’s doors can be removed, which can be useful off-road where it gives drivers a better view of the road around them.

For someone like Bianca, a 21-year-old nanny from Los Angeles whom Ford credits with inspiring the idea of storable doors, the appeal of taking the doors off was simply to enjoy the warm weather and a feeling of freedom. But there was an issue.

“For her, the difficulty of taking the doors off a regular truck and lack of anywhere to put them seemed like an inhibiting factor,” Paul Wraith, the Bronco‘s chief designer, told Automotive News. “It led to a good idea.”

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Ford realized that not all of the people who wanted to use one of their features might have been able to, so they went to work giving four-door Bronco owners a place to store their doors all of the time. Unfortunately for them, it turned out to be hard work.

First, the trunk had to be made wide and long enough to hold four doors. Although they could have simply extended the truck, that would have interfered with the departure angle, a pretty important feature for an off-roader.

Then there were the smaller issues of design that made the doors challenging. They have to be light and small enough to carry without being fragile or too small for owners to easily get in and out of the cabin. They also had to keep features like armrests without becoming unwieldy when it came time to move them. That wasn’t the hardest part of the design, though.

“Mirrors are among the hardest part to design on any vehicle,” Wraith said. “Challenging ourselves to do what we did… we had to keep the door [design process] open for a little bit longer before we nailed it.”

Designers had to work on obvious stuff like placing the mirrors where they wouldn’t be blocked by the A-pillars and also on the subtler stuff, like placing them so that the grab handles didn’t block drivers’ sightlines. It meant a lot of massaging and a lot of trial and error to get it all just right.

Ford was also sure to add a QR code to the bags to help drivers out if they ever got confused halfway through the process. And to ensure that they could always remove the doors, which are held on by two screws and a bolt, they added a toolkit to the vehicle.

“Doing stuff that’s new is scary because you have nothing to copy,” Wraith said. “We all had to take a big brave pill, feel very confident we’ve made the right decision and then use all our talent and energy and passion to deliver it.”