Lorna Gold, head of policy at aid agency Trocaire, perhaps put it best.
Signing a deal is one thing, the test is what actions come next, she said.
She was speaking shortly after almost 200 nations agreed to ratify the Paris Agreement to address climate change at the 21st Conference of the Parties (COP21).
'Historic' is an often overused term, but this deal deserves such a description. Never before, despite 20 previous COPs, has the global community come together to tackle such a pressing issue.
For two decades, the science has warned that our climate is changing. But national self-interest prevented a common approach to action, even as a series of increasingly alarming reports from the UN's Intergovernmental Panel on Climate Change (IPCC) spelt out in detail how the ice caps were melting, sea levels rising, greenhouse gas emissions reaching record levels and rainfall patterns changing.
In 2009, at COP15 in Copenhagen, a deal slipped out of sight after the Danish hosts lost control of the process. COP21 was a second chance. French diplomatic skills were brought to bear, and incredible attention paid to detail to ensure the event ran smoothly.
Staff couldn't have been nicer. The food at the conference venue was excellent, and the toilets spotless. Each person was given a re-usable water bottle to refill from coolers to help prevent waste, and delegates moved through airport-style security at the conference venue quickly.
There were some wonderful, typically French moments throughout the week. On Saturday, when a deal was still in doubt, the parties broke for lunch before the final plenary which would dictate whether agreement had been reached.
Earlier in the week this reporter, having finished a nice dinner in a city centre restaurant with a colleague, spotted a mouse running around. In Ireland, you'd refuse to pay and complain to the HSE. In Paris, it would be disappointing if a mouse wasn't present.
The organisers also made access to the city and conference venue as easy as possible.
Free travel passes were provided, allowing people access the extensive - and low-carbon - electrified Metro and RER train system.
Public transport hubs had directions to the lines which would transport people to Le Bourget train station, where they were ferried by hybrid bus to the conference venue.
Paris aims to have an electrified, low-carbon transport system before 2020, and what better place to show off the art of the possible than to a captive audience in the city to discuss climate change.
But it was no holiday. The negotiating process was long and difficult, with many unsung heroes involved.
Linguists were employed to help agree a form of words, as parties argued over whether 'should' or 'shall' were included, for example.
The Irish delegation included officials from the departments of environment, finance, foreign affairs and agriculture, as well as the Environmental Protection Agency, Sustainable Energy Authority of Ireland and Office of the Attorney General.
They helped negotiate technical aspects of the deal over 12 days and three all-night sessions.
By the end, they knew all about running on empty and surviving on sandwiches and coffee.
In fact, just before the accord was adopted, a series of legal changes had to be made to the text because, as the last plenary was told, it was drafted by lawyers functioning with little or no sleep.
Environment Minister Alan Kelly, who led the delegation, paid tribute to officials, saying the country should be "genuinely proud" of them.
"At key moments late in the night, they were crucial in maintaining political momentum behind a deal," he said.
"I was very proud to have them with me as minister. They have served their country and department well."
Not everyone is happy with the final text. Friends of the Earth described it as a "sham", while Niacaragua said it was "kicking the problem down the road".
Professor John Sweeney, from Maynooth University and who was part of the IPCC team awarded the 2007 Nobel Prize, said the potential in the agreement was 'huge'.
"We don't want to go back moaning and groaning," he said. "Nobody got everything they wanted, but that always happens in negotiations. The potential of this agreement is huge, and the ratcheting up (of targets) is very positive.
"It's historic because I don't know of any other agreement involving the 196 nations in the UN, certainly not in this area. It's quite an achievement when you think of all the disparate countries involved."
There is disappointment that the agreement - as opposed to the preamble - doesn't make explicit reference to human rights, but it does include a reference to gender, an important addition as most of the world's farmers are women who are among the most affected by crop failure caused by climate change.
Key to its success will be the response of business and investors.
The Paris Agreement means oil, gas and coal have no long-term future, and it will be interesting to see what impact it will have on share prices in the short-term.
There were many moments when it appeared the parties were moving further from a deal, rather than closer.
Some fossil fuel-producing countries suggested they would have to be compensated for leaving their oil in the ground.
There were calls for vulnerable countries to be compensated for loss and damage caused by climate change, which bigger emitters like the US opposed.
Some of the left-wing Latin American states indicated they shouldn't have to do anything at all, as the West had caused the problem in the first place, and even right at the end Malaysia was threatening to scupper a deal, while Africa was arguing it was among the most vulnerable, meaning it was entitled to more finance.
But, more than a day late, a deal eventually came.
When COP president Laurent Fabius opened the last plenary to the floor, he said the words that so many had waited so long to hear: "I see no objections. The Paris Agreement is adopted."
And with that, the tide of history had turned. What happens next will dictate whether those late nights were worth it.