I believe Boris Johnson got carried away by all the initial hype surrounding his premiership and the adrenalin-inducing drama of getting Brexit done. Somewhere in the distance of his brain I think he saw himself going down in history as a sort of Churchillian figure presiding over an historic moment in British history.
... as opposed to being wholly committed to Brexit for its own sake.
Not for him the burning of the midnight-oil pondering over the minute details of a complex, far-reaching constitutional change - allegedly anything more than two sheets of A4 would challenge his attention span. He wanted to be the focus of public attention as he made his way round the country grinning, gurning and ruffling his hair, charming the elderly and firing-up white van man, and all in between!
Those who actually knew him, worked with him, employed him previously - they knew. They knew that he was all fur coat and no knickers. So to speak.
However, if you're a Boris-believer, it's a commitment - and for quite a few, it's for life. So some Tories, in desperation at the prospects for the Party come election time are casting around desperately looking for something or someone to reverse their flagging popularity.
Kwarteng (a Boris-believer) sensing the writing on the wall is going to bog off, and he's already making thousands of £s elsewhere - from media appearances and is about to become an advisor to an Australian mining company. His parting gift to the Party is to recommend Mr Brexit be taken backinto th fold. Byeee - thanks for crashing the Pound by the way!