The Banking Inquiry has been told that former Finance Minister Brian Lenihan felt he could not believe the advice given by his own advisors.
Economist David McWilliams said that he was called by Ministers in both Fianna Fáil and the Green Party because they could not trust or believe the advice they were given.
He says that made the bank guarantee necessary - in order to buy time and establish the full facts of the banking crisis.
He has told the inquiry about one meeting with Brian Lenihan where concerns about the banks were first beginning to emerge.
"The most important thing in all these crises is to establish the facts," he said.
"And I said to him, I said: 'Do you know the facts? Do you absolutely know what's going on?'
"And he said: 'No'. He said: 'I am getting different numbers all the time'."