Johnson's determination to get brexit done and to have 'a clean break from Europe' on terms which involve other countries happily returning fishing rights they bought from us (without recompense for the said previous purchase) in addition to the EU accepting terms they don't feel create a level playingfield and risk their economic future make any deal impossible. Our demands simply aren't achievable.
The alternative is adherence to the Withdrawal Agreement in which we are unable to bail out businesses via state aid and to have no deal which creates huge trade barriers and tarriffs overnight and massive customs red tape which we simply are not yet prepared for because the systems for running this are running behind schedule. This would lead to massive food shortages and Brexit lorry parks throughout the country for the forseeable future.
Johnson's latest bright idea is that he seems to think he can avoid chaos by a strategy which would cause even more chaos by deliberately reneging on the withdrawal agreement which is an international agreement just months after throwing a hissy fit for China doing exactly the same thing. This wouldn't just be hypocritical but would make a mockery of our credibility internationally and potentially endanger every other international agreement we've currently in place because well, why should anyone else stick to an agreement with the UK.
We could face years of legal wrangles with god knows which countries and businesses suing the British government.
But y'know Johnson thinks this is a sensible strategy and a cracking plan to force Brussels to blink first rather than actually take the subject seriously and do something in the country's interest rather than prevent Johnson from damaging his internal reputation with leave voters and because he thinks this is the correct hill to die on to prove he doesn't govern by u-turn. Johnson's ego seems more important to him than feeding the nation and having an international reputation.
Or he could do another u-turn.