And politicians who say otherwise are being "arrogant"...
"I have no faith in the politicians in London going on about how 'the world will want to trade with us.' The world will want to screw you - that's what happens in trade talks," Ryanair chief executive Michael O'Leary said, in his latest piece of Brexit commentary.
The outspoken Irish businessman added that the predictions of UK politicians expecting favourable outcomes from the process is "arrogant nonsense."
He spoke as the airline announced new routes from Northern Ireland which are due to deliver 1.1 million more passengers flying to and from the region annually.
Mr O'Leary criticised the Stormont Executive's decision to give £7m in aid to Derry Airport. Ryanair has dropped its Derry to London route and is scaling back its other operations at the airport.
He questioned the future viability of the airport and said that cutting airport passenger duty would have been a more efficient means of boosting business in the region.
The Ryanair boss added that current government charges are resulting in Northern Irish travellers choosing to fly from Dublin instead.
The Irish Government did have a similar tax but it was abolished in 2014.