His remarks are nonetheless a headache for the British Conservative leader who is trying to rally support for her Brexit plan, which would see Britain remain closely aligned with the European Union on trade rules for goods (though not services).
Boris Johnson watched from the Tory backbenches on his return to the Commons following his resignation as foreign secretary over Brexit.
May won votes on a customs and a trade bill in Parliament earlier this week, but suffered an unexpected defeat on a separate amendment, which means her government must now seek continued participation in the European medicines regulatory framework.
A bristling Mrs May insisted at "absolutely no point" had that happened because "Brexit continues to mean Brexit".
Mr Johnson used his resignation statement in the Commons to call for the PM to abandon her "miserable" version of Brexit, Mrs May's former joint chief of staff Nick Timothy said the current situation was "deeply depressing".
Mr Johnson quit Mrs May's Cabinet on Monday last week, declaring that the plans for the UK's post-Brexit relations with Europe which she set out at Chequers would leave Britain a "colony".
With May's support faltering, members of her own party, including Davis, felt emboldened to ask critical questions about her way forward.
Also in the chamber was another recently-departed minister - Boris Johnson.
In the past 18 months, said Johnson, "it is as though a fog of self-doubt has descended".
She said she wouldn't have time to listen to it before a meeting with her backbenchers last night as she would be busy catching up on paperwork.
The close shave in parliament was May's third this week, underscoring the difficulty she faces in passing legislation on one of the most divisive and important decisions in modern British history with only a minority government and her Conservative Party at war with itself.
Johnson told lawmakers that the government had "dithered" and failed to make the case for a free trade agreement outlined in the January 2017 speech at Lancaster House in the heady months after the referendum passed.
Mr. Johnson said that the United Kingdom should aim for the vision of "a strong independent, self-governing Britain" set out at Lancaster House, not the "miserable, permanent limbo" of Chequers.
While the House of Commons debates these texts, the European Commission is analyzing the plan for future trade and customs relations it received from the United Kingdom government, the survival of which depends largely on the response from Brussels. "We have to have a compromise position that enables the country to get an agreement with the European Union", trade minister Liam Fox told BBC radio.
"Failure to keep our promise to the electorate will nearly certainly lead to the catastrophe of Jeremy Corbyn becoming Prime Minister and I can not sit back and allow that to happen".