The trading deal negotiations - which are just that, nothing cut and drieduntil they are over and signed - will be between, on the one hand, countries or trading blocs which have existing deals with many customers and suppliers, and on the other, a UK which has torn up its membership of one of the largest and most influential trading blocs in the world and will be asking to be let in to trade in competition with those existing agreements.
The "big boys" of world trade - the US, China, etc - play to win, regarding a deal as something that is win or lose - they win, we lose.
I am not even going to start on the other results of going back past ???? years of international co-operation, free travel between countries and over borders without visas and customs formalities and delays, social welfare legislation, educational exchanges , blah blahblah. And as for NI . . .