First Minister Rhodri Morgan has urged people in Wales to embrace a "can-do" attitude.
Mr Morgan said the best days "are yet to come"
In a speech to the Institute of Welsh Politics conference in Cardiff, Mr Morgan said the country was blighted by outmoded, negative perceptions.
He told BBC Wales: "We haven't somehow developed the self-confidence about ourselves that goes with the facts".
But Plaid Cymru said the public would not believe Mr Morgan's "rhetoric" that things were getting better.
The speech was the first of six Mr Morgan will make between now and the run-up to the assembly elections.
Mr Morgan wants to dispel the perception that Wales is a country that does not get things done, and used the Wales Millennium Centre, the Millennium Stadium and the Senedd building to make his case.
He told BBC Wales that, when outside Wales, he heard constant praise of Wales' achievement in constructing the landmark buildings in Cardiff.
He said construction executives marvelled at how this had been achieved for "less than the cost-over run" of the new Wembley stadium, which unlike the Millennium stadium will not have a roof.
He said: "I think we just haven't realised, as a country, just how much people outside Wales are re-rating us as a can-do country, and turning to us, because they can see we can solve problems, that others haven't.
"And the only people who haven't really appreciated that are us in Wales, ourselves."
He added a typical false perception people in Wales might have about their country was that the number of jobs had fallen since the Welsh assembly was created in 1999.
He said 126,000 new jobs had been created since that time, a rate of increase of 10%, which was even higher in west Wales and the south Wales valleys.
He said: "I'm only asking people to look at the facts and look at the evidence - not to talk Wales up but to stop talking Wales down.
"I think the evidence and the facts do show that Wales is developing a can-do culture, and a can-do culture reputation outside Wales.
"It's just that we haven't somehow developed the self-confidence about ourselves that goes with the facts."
Another subject Mr Morgan is expected to say that it is a myth that the Welsh language is a language of the past and is in decline.
He is also set to focus on the Government of Wales Act 2006, claiming it offers new opportunities, and that the best days are still to come.
BBC Wales' political correspondent Guto Thomas said the speech was an attempt to set out an agenda ahead of the assembly elections.
But Mr Morgan's comments were attacked by Ieuan Wyn Jones, leader of Plaid Cymru in the assembly.
He said: "The stock of politicians amongst the Welsh public is pretty low and they are not going to listen to people like Rhodri Morgan telling them that things are getting better.
"The reality is that the experiences that they have day-to-day, in their own homes, in the schools, and the hospitals and in the workplace just doesn't match up to that rhetoric."
Nick Bourne, Conservative assembly leader, said: "You will never get me knocking Wales - I will knock Rhodri Morgan as long as I have life and breath. I think he has done immense damage to Wales."
Welsh Liberal Democrats assembly leader Mike German added: "Labour's theme tune used to be Things Can Only Get Better. Now it seems that Rhodri Morgan's theme tune for next year will be Always Look On The Bright Side Of Life.
"His government has run out of energy and ideas, and no amount of whistling a happy tune will convince the people of Wales that we live in the best of times."