Sonder cofounder said pulling off Marriott deal was the 'hardest thing' he's ever done. Now he's left shocked.

• Sonder's downfall has stunned the short-term rental company's cofounder. • "I've poured my heart and soul into building this company," Francis Davidson told Business Insider. • Davidson previously said pulling off Sonder's deal with Marriott was the "hardest thing."

For the short-term rental company Sonder, teaming up with Marriott was a lifeline.

In a LinkedIn post about five months ago, the San Francisco firm's cofounder, Francis Davidson, said that pulling off the Marriott deal was the toughest challenge he'd ever faced.

"Making this deal happen — along with the multi-party, complex capital raise I orchestrated — was the hardest thing I've ever done," Davidson wrote in the June post commemorating his last day as the company's CEO.

Now, Davidson told Business Insider that he's