Colin Barnett says politicians have "fallen into the trap" of being "too specific" about election promises before they are in possession of all the relevant information.
The Premier made his comments during an interview on ABC radio yesterday where he was forced to defend the slippage of time lines around major transport projects promised by the Liberal Party during the March election campaign.
"I think one of the problems that's happening in election campaigns now is that if you say you are going to build a project, a museum or whatever it might be, people, the media then (ask) 'Well, give us a date, give us a start time'," Mr Barnett said.
"The reality in both Government and the private sector (is that) projects rarely run exactly (to schedule) and I think as politicians we've fallen into the trap of actually being too specific, making all sorts of detailed announcements about projects in election campaigns without really having the information available."
During the election campaign, the Government promised the $1.9 billion MAX light rail system and the $2 billion airport rail line would be delivered by the end of 2018.
Just five months later those time lines were pushed out to 2019 in the August Budget, and further delays are likely to be announced later this month in Treasurer Troy Buswell's midyear review.
Opposition Leader Mark McGowan said the Premier's comments were extraordinary.
"He said a few months ago that people don't look at the literal promise the Government's made, he then said people don't read the promises that were made before the election," Mr McGowan said.
"The Premier was not forced into making these promises, he volunteered them . . . the Premier made these promises of his own volition, the Premier needs to man up and stop blaming other people."
Notre Dame University political analyst Martin Drum said the Liberal Party's claims about a "fully funded, fully costed" election plan had set the bar higher.