The biggest problem for each of our past three prime ministers was they turned out to be someone other than the person we thought we'd elected, and we couldn't forgive this breach of trust. Let this be a lesson for Malcolm Turnbull, writes Michael Bradley.

Looking back on the wasteland of the past three prime ministerships, the benefit of hindsight obscures a critical perspective: in the case of each leader, there was a moment when it became clear that they were going to fail. And, in each case, the failure was a breach of trust.

This is the key to understanding why we keep losing prime ministers and how it could be different.

For me, the turning point for each prime minister was as sharply obvious as that moment in a game when the ball is dropped, the shoulders slump, and the momentum shifts irretrievably the other way.

Kevin Rudd came to office on a wave of anti-Howard optimism, and his signature belief was that climate change represented "the greatest moral, economic and social challenge of our time". Julia Gillard stated before the 2010 election that no government she led would introduce a carbon tax. As for Tony Abbott, well, he said a lot of things but nothing cut through like his unequivocal 2013 election promise that there would be no cuts to education, health, the ABC or SBS, and no changes to pensions or the GST under his government.

Each of these undertakings was breached, but it isn't the breaking of a promise alone which does in a prime minister. Every PM has broken promises, repeatedly. John Howard famously survived his "never, ever" line on the GST and went on to 11 years in office.

The difference is in the gap between what the public was expecting and what it received.

Rudd sold himself as an agent of hopeful change with a long-term perspective on the public good. Climate change was at the centre of this outlook. More than half the population agreed with him, but everyone understood the depth of his personal conviction. When he unexpectedly dumped the ETS plan in 2010, he discarded along with it all of his credibility.

The public was prepared to tolerate Rudd's awkward dorkiness and the general impression that he was a bit full of it on the promise that he was genuine. He betrayed that bargain, leaving the residual sense that he had no convictions at all.

Gillard's deal was different. She took the job in the dead of night, and had a tough time from the start trying to establish legitimacy. Nevertheless, she won enough of the 2010 election to form government. The circumstances of her elevation with its whiff of treachery, combined (we should all admit) with her being a woman, meant that she had precious little trust to play with. She sacrificed all of it and more when she did the carbon tax deal with the Greens. Necessary as it was for her government's survival, it was fatal for her standing with the voters.

Nobody ever liked Abbott. However, he promised to be everything Labor had not been: plain speaking, no surprises, probably boring but at least predictable. His litany of promises exemplified that approach. Everyone knew he couldn't deliver on everything he'd promised, but we figured he'd probably just do not much at all.

Then the 2014 budget landed on us, straight from some weird neo-conservative think-tank heaven, setting out the most radical agenda any of us can remember. Broken promises littered the landscape, but the lethal core was that we'd been promised a comfortably conservative government and instead woken up to find a pack of raving ideological zealots in our bed. We all thought Joe Hockey was a nice, affable guy! Turned out he'd been chewing cigars and wanted to push responsibility for Australia's debt burden onto the poor. We already knew Abbott was very odd, but we'd assumed he'd restrict himself to doing weird stuff on the fringe, not try to fundamentally rewrite our social compact.

In each case, the fatal breach of trust was not the broken promise about policy, but the destruction of our faith in the promise of the person. Each of Rudd, Gillard and Abbott turned out to be someone other than the person we thought we'd elected, and we could not forgive them for that.

There are two distinctly common elements to the people that these failed prime ministers turned out to be.

The first is the process of governing. None of Rudd, Gillard or Abbott appears to have understood how functional, effective decision making needs to occur in a parliamentary democracy. Our governmental system is one of consensus; that arises from the electoral process. We elect local members; they form parties; the elected members elect their leaders; from among them, cabinet is formed; policies are developed and decisions made by building consensus within that multi-layered organism. This can only work with very good internal governance.

Australian politics has drifted in many respects towards the US presidential style. The traditional cabinet process of policy development has evolved into the kitchen-cabinet decision-making that Rudd and Gillard preferred and ultimately, in Abbott's government, to autocratic decree directly from the Prime Minister's Office. The fact that Abbott's cabinet ended up with literally no business on its agenda says it all.

The second part was entirely missing from Australian politics for the past eight years - leadership. Rudd thought leadership meant being extremely busy doing and announcing things; Gillard thought it meant being the hardest working kid in the class. Abbott seems not to have thought about leadership at all, beyond just wanting to have it.

They were all wrong. We look to our leaders, whether in politics, business or sport, for one thing above all else: inspiration. We want to be assured they know what they're doing, that they won't panic when things go wrong, that they'll work hard and get in the trenches with us, that they'll be consistent and honest and true. But none of that matters if they don't inspire us to follow them. Seldom did Rudd, Gillard or Abbott say something genuinely inspirational. They saw leading variously as an honour, a reward, an ordeal. They did not grasp it for what it really is: an opportunity to embrace and influence change.

Malcolm Turnbull understands all this; it's plainly stated in the speech he gave announcing his challenge for the leadership. He focused heavily on promising a return to proper cabinet government; and he has been consistently using language of positive optimism, acceptance and embrace of change and excitement about what that means for Australia. He said these are exciting times; he's right, they are.

Turnbull has promised something new: inspirational leadership based on a positive view of the world and all its possibilities. Cynics will gather like locusts around this idea, willing it to fail, and Turnbull has set himself up for another short prime ministership if he turns out to be just another retail politician. I don't know what he is but I know that, if he delivers on his promise, he could have the job for a very long time.

Michael Bradley is the managing partner of Marque Lawyers, a Sydney law firm, and writes a weekly column for The Drum. Follow him on Twitter @marquelawyers.