It's a notoriously hard thing to measure, but when it takes hold, a drop in confidence poisons growth. Companies stop investing or hiring new people until they know what lies ahead.
New Zealand has been cocooned from the worst effects of the trade wars, thanks to distance, an FTA with China, and relative predictability in commodity prices - until now.
O'Sullivan says we could be on the verge of a crisis.
"Whether it's a financial one I'm not so sure. Clearly, protectionism is on the rise again, and from a New Zealand export and trading perspective, we need to be nimble."
As the economy gets crimped in places like China, middle-class consumers won't be able to buy high-value products, people won't travel as much, and they won't send their students abroad.
The latest ANZ Business Outlook Survey had "nothing good to say" about business confidence in New Zealand, as it hit the lowest level in more than 11 years.
It's not just the US and China in a trade war, but also South Korea and Japan.
"What we're seeing is a number of big players misbehaving in a very serious way," O'Sullivan says.
Until now, we've had "golden weather" for New Zealand's trade policy. We've had an enforceable international trading system, increasingly open markets, and a bipartisan approach on trade.
But in the past three years we've had some real challenges on all three of those fronts, Vangelis Vitalis says.
We have to be nimble and play our part in defending the international rules of trade that protect small countries like New Zealand, Vitalis says.
"One of the challenges for New Zealand is sustaining our own levels of exports, but crucially making sure the markets internationally don't start to close on us ... and we are seeing disturbing signs of just that."
By December we could have a World Trade Organisation (WTO) - the body that enforcers the rules - unable to function properly if the US won't approve new judges.
"No question this is a very serious situation we're in," Vitalis says.
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But Peter Petri, founder of the Brandeis School of Business in Boston, and senior fellow at the Brookings Institute is quietly confident.
The international system is a mess, but it hasn't collapsed yet, he says. Big countries can survive trade wars by the sheer force of their markets, but small countries that have to import more products than they export are at risk.
There's no such thing as the perfect trade deal, and trade agreements won't suddenly make your life better, but if New Zealand is going to weather this crisis, it needs to play on every field.
That means chasing good-quality bilateral deals where it can't get agreement on multilateral deals.
Vitalis says the big lesson he learned from leading CPTPP negotiations, was that New Zealand's expectations of trade agreements are very wide now.
"They want to be reassured that sovereignty is preserved.
"That governments have the right to regulate in favour of pharmaceutical pricing, IP rights, or the Treaty of Waitangi. They want to know that all those things are preserved, and that became a real priority for us."
Despite the drop in global confidence, he's hopeful about the future.
"The biggest risk is not a 'Big Bang' crash, but more of a gradual disintegration, and that's where the urgency really lies, in preventing that disintegration from going too far, so the rot doesn't set into the foundations of the system.
"That's where I am really quite positive that New Zealand can help shape what will become the new world order."
