The most significant problem the Government encountered during its efforts to get the two Nice Treaty referendums passed was fear, Mr Ahern told leading Isle of Man businessmen last night.
"Some of the fears that people held had no basis in fact," said Mr Ahern, speaking to the Isle of Man Euroclub at the Mount Murray Hotel, during a four-hour visit to Douglas.
"These fears were genuine and represented realities in the minds of many. We learned that we had to deal with every fear systematically and honestly. And we learned that in answering every fear, we had to respect the legitimacy of having the fear in the first place," he said.
He said he had discussed the operation of Sellafield and shared worries about the shipment of nuclear cargoes through the Irish Sea with the Isle of Man's Chief Minister, Mr Richard Corkhill.
The Isle of Man is an internally self-governing dependent territory of the British Crown, which is neither part of the United Kingdom nor a member of the European Union.