When the DUP formally backed Brexit in 2016 they were pretty sure that Leave wasn't going to carry the day. And they were 100% certain there wouldn't be a Leave majority in Northern Ireland. But the referendum meant voters going to the ballot box and the DUP is always sourcing ways of building and expanding its electoral base; so there seemed to be no particular risk in taking a pro-Leave position three months before the 2016 Assembly election - which was a few weeks before the referendum.
Playing the UK sovereignty card, they reckoned, would reap electoral dividends; especially since the UUP were pro-Remain.
Anyway, their pro-Leave position wasn't terribly emphatic: 'The DUP has always been Eurosceptic in its outlook.
'At every stage in this European negotiation process (David Cameron was scurrying around EU leaders at the time) we had hoped to see a fundamental change to our relationship with Europe. (But) in our view we see nothing in this deal that changes our outlook.
'Therefore we will, on balance, recommend a vote to leave the EU. As every voter has the opportunity to express a view we fully expect that DUP members and voters will hold a range of differing personal views as to what is in the best interests of the United Kingdom. They are fully entitled to do so during what will be a momentous political campaign about the direction of travel our nation chooses.'
Reading those comments today - just over two years after Arlene Foster made them - I'm struck by how measured they are.
None of the rhetoric we were used to hearing from the likes of Farage, Johnson and Gove. Nothing more than an 'on balance' conclusion to Leave and no hard pressure on party members and supporters to follow suit.
In essence, the sort of response you'd expect from a party leader who probably reckoned there was no point getting terribly excited - or even internally fractious - over an issue which was probably going to be rejected by the UK electorate.
So June 23, 2016, came as a huge shock. The DUP suddenly found itself having to support an outcome it had neither expected nor planned for. More than that, it also dawned on the DUP leadership that the outcome brought potentially huge constitutional challenges for the UK in its wake; as well as upending the entire dynamics of the relationship between London/Dublin and Belfast/Dublin.
If ever there was a moment for cautious words and thought-through responses, it was then. And, in fairness, for the first few months the DUP did play a careful hand.
But everything changed with RHI, the collapse of the Executive, the loss of the overall majority in the 2017 Assembly election, the ongoing impasse here, the increasing toxicity of the relationship between the DUP and Sinn Fein and, of course, the DUP's totally unexpected elevation to the position of king-maker in Westminster.
Once again the entire dynamics of the East-West, North-South relationships were upended: although this time the DUP decided that with a Prime Minster as their hostage/ally they could become much tougher and more belligerent.
Mind you, there is a feeling within sections of the DUP at local level that the new toughness and belligerence is being driven by the MPs rather than the Assembly bloc.
The problem for the DUP is that Mrs May is a weak and crippled Prime Minister who finds herself in the Nanny McPhee position of needing, but not wanting, the DUP as her only prop. That makes her an unreliable ally.
She needs to make deals with her divided cabinet, her divided backbenches and her divided grassroots, as well as fending off an increasing number of defeats in the House of Lords and ambushes in the Commons.
Not to mention the general problems with the EU 27 and the particular problem with Ireland. In other words, the DUP doesn't and won't have her full attention.
The other problem for the DUP is that the relationship between unionist parties and successive Conservative governments hasn't been all that good since the early 1970s.
The DUP will be well aware of that litany of broken promises, u-turns, betrayals, sell-outs and treachery, because it was the DUP which outlined them in great detail when the UUP announced their electoral pact (UCUNF) with David Cameron in 2009. As I say, May needs them for her everyday survival; but it can't be taken for granted, which the DUP won't, that she won't ditch them if she has to.
It's in the interests of Northern Ireland to have a good working relationship with both London and Dublin; so it makes sense for the DUP to promote and cooperate with both governments, and with the EU's chief negotiator, Michel Barnier, in a deal that meets the long-term interests of all of them.
The DUP must ensure that it doesn't put itself in the position - and that means a knock-on effect for Northern Ireland - of forcing the Prime Minister (and it may not be Theresa May when the crunch moment comes) or House of Commons to choose between DUP concerns and wider UK concerns and interests. Or worse, finding itself in a position where the Conservatives have to make a choice between their own survival and the DUP's.
The DUP also needs to abandon its present fixation with a 'troublesome' Irish government. Leo Varadkar and Simon Coveney aren't responsible for the present crisis.
Their recent input into our local politics has been caused by two outcomes, neither of which they provoked: the failure of the DUP/SF to cut a deal, and the UK's decision to leave the EU. Both of those issues have a direct impact on the Irish government, so it would be quite remarkable if they didn't raise their concerns.
But, let's be clear, Varadkar and Coveney have no interest in formal Irish unity, let alone annexing Northern Ireland.
They have enough other problems on their plate without risking the catastrophic fallout from trying to detach Northern Ireland from the United Kingdom.
Yes, unity may appeal to them at some point: but this is nowhere close to that point. They are not that stupid.
Dublin didn't want the UK to leave the EU. They don't want a deteriorating relationship with NI or the UK.
They want a deal - because it is in their particular interests - which suits London/Dublin/Belfast and they are quite content for NI to remain an integral member of the UK, as per the Good Friday Agreement arrangements.
The DUP can be and should be instrumental in creating that deal, and should play that hand with Mrs May. This is the party's biggest challenge since it was founded in 1971; bigger, much bigger, than the deal to form a government with Sinn Fein in 2007.
Failure is not an option.