It is a question which has vexed many since last year's Labour Party conference in Dunedin, when Mr Robertson declared to party faithful that Budget 2019 would be the "Wellbeing Budget".
In a world which still largely thinks of Gross Domestic Product - the total value of the goods and services produced by a country annually - as the economic be-all and end-all, Mr Robertson pledged to change the definition of what counted as economic success.
Instead of dollars and cents, the Government will instead measure policies against "wellbeing criteria"; progress in improving mental health outcomes or reducing carbon emissions being as relevant as the deficit or overseas borrowing.
"Everyone has got their own definition of wellbeing, but it is essentially people being able to lead lives of purpose and meaning for them, and to have the capabilities to do that,' Mr Robertson said.
"It is also a sense that our wellbeing is not just determined by our incomes, either as a country or as individuals.
"That's important - we need to generate good paying jobs and we need the country to be prosperous, but a wellbeing approach means we care much more about who shares in that prosperity and how we maintain and sustain it for the long term.
"I like to bring it down to a person's life and what we can do for them to be able to live that life with purpose and meaning."
Which all sounds well and good, but how exactly can you measure that?
Treasury has had a go and constructed a "Living Standards Framework," the foundations of which are four pillars: natural capital, human capital, social capital and financial and physical capital.
Under those groupings will be around 60 indicators, which will be monitored regularly.
It sounds vague - it lacks the solid familiarity of Treasury's traditional indices - but Mr Robertson predicts we will get used to the change.
"It is more difficult as some areas are not as easy to define, but doesn't mean they are not important.
"While we may not be quite as used to the measures as we are with GDP, I think actually because the totality of them represents the values of New Zealanders, I think over time people will be able to relate to them more.
"But there will be some very specific targets; this Budget will be the first Budget where we measure child poverty targets, that has been put in to law."
That has made this year's Budget bidding process, where ministers present their funding requests, tougher, Mr Robertson said.
With new criteria to be gauged against, new spending had to go through more hoops and undergo a deeper analysis than for his first Budget.
That first Budget in 2018 was very much the work of a new finance minister in a newly-elected government.
With a firm adherence to self-imposed Budget responsibility rules, it was a "steady as she goes" Budget, which hoped to strike a balance between maintaining business confidence and satisfying Labour's base.
The Wellbeing Budget will be much more a demonstration of Mr Robertson's own political philosophy.
Even if he is quick to point out governing partners the Green Party and New Zealand First had their say, as did the Prime Minister and his Labour colleagues, if the promised radical rethink is even half as far-reaching as envisaged, the Wellbeing Budget will be inextricably linked with Mr Robertson personally.
The personal aspect to these politics had a lot to do with Mr Robertson's South Dunedin upbringing, which he credits for having shaped much of his economic philosophy and his reasons for being in politics.
"What I feel I learned there was a grounding in the importance of social justice.
"South Dunedin was an amazing place to grow up, it was a hugely strong community with a real neighbourhood feel to it ... a lot of the parents worked at Hillside or the freezing works or whatever, so it wasn't wealthy in financial terms but it was wealthy in terms of its community spirit.
"[In] My own background growing up in the Presbyterian Church, there was a focus from my parents around social justice and concepts like you should treat others the way you wish to be treated. We are our brother and sister's keepers - those things mattered to me and they have definitely influenced who I am."
So did his time at the University of Otago.
Mr Robertson is speaking in the quadrangle, with the student union he led as president behind him, the registry building he and several other students once occupied in a noisy protest is to his side, and the political science department where he got his BA with honours in front of him.
"I learned a lot from my degree and I also learned a lot from being part of OUSA," Mr Robertson said.
"Like everybody in life, things develop over time, but I'm not taking sole ownership of this - it is also a reflection of the Labour Party's values but also New Zealand's values."
Mr Robertson and his colleagues have done a great deal of reflection on what the phrase "New Zealand's values" means over the past few weeks.
As a senior Cabinet minister and the most senior government figure in Wellington when the March 15 terror attacks took place, Mr Robertson immediately knew he was at the centre of a significant moment in New Zealand history.
This was a moment which even a long political apprenticeship working in MPs' offices before becoming a parliamentarian and a minister cannot prepare you for, he said.
"It was an experience that none of us wanted, and while you know if you are going to spend a long enough time in government that something major will happen - perhaps a major disaster or something like that - I don't think anyone could have foreseen this and the scale of this, so it was a very difficult time to go through.
"I think it's about applying your ethical values to those situations, which is what I think the Prime Minister did magnificently in her leadership, which was to apply the values of kindness, of inclusion, and say that is how we are going to respond to this - we are not going to respond in a negative or a kneejerk way, we are going to say how do we bring our community together."
Work on the Wellbeing Budget was fairly well finished before March 15, but it will contain some material directly in response to the attacks.
There would be more, Mr Robertson pledged, but the Government needed to await the outcome of the Royal Commission into the attacks, and also decide where best to place its efforts.
"There is only so much of that which is about budgets - a lot of that is about how we go about what we do as a government.
"It does fit with well-being; one of the big concepts of wellbeing is this concept of social capital, or to put it in lay person's terms, community strength, and I think that is an area that for a long time we haven't paid a lot of attention to as a society, and it is now part of our framework for measurement and therefore will be part of our framework for what we invest in."
Gauging the success of any such changes will be the work of years, maybe of decades, and that ultimately was the philosophy behind the Wellbeing Budget, Mr Robertson said.
Changes would be made, but the outlook of those changes was intergenerational rather than a year or an election ahead.
"That is at the heart of the wellbeing approach and I hope people will see the beginnings of that," he said.
"I have always said it is a work in progress, we're not going to completely change the way we do things in one year.
"But in particular areas people will see that we have changed our approach and that we do have that very long-term view of what we need to invest in now to get benefits later on.
" I hope it will give people a much richer picture of us as a country and where we are today."
