I think this is pretty close to what's happening:
Shadow foreign secretary Emily Thornberry said Boris Johnson's resignation was about his "leadership ambitions".
She told BBC News: "They are not just two senior cabinet ministers, this is Brexit.
"This is because for the last two years we have just been seeing a soap opera playing out in the Tory party.
"We have not been seeing the party that is supposed to be in government thinking about the country, but only thinking about themselves.
"I have been saying to him: concentrate on the day job, Boris - think about Yemen, think about peace int he Middle East... stop thinking about your leadership ambitions and think about your day job.
"And this is about Boris Johnson going for the leadership because he is worried that someone else has gone for it first and he feels he has to catch up."