Last week’s election appears to be bringing the first phase of Brexit towards a close.

The resounding majority won by the Conservatives sets the door wide open for the ratification of the Withdrawal Agreement Bill, which in turn will result in the UK’s withdrawal from the European Union on 31 January 2020, some four-and-a-half years after the referendum.

But as I’ve been saying for a long time now, that is only the smaller, easier part of Brexit, as we start to consider what the future relationship between the two might look like.

With that in mind, what lessons might we learn from the first phase, to help us navigate the rest of it all?

Firstly, I’ll invoke my first rule of Brexit: it’s always a bit more complicated than you think it is.

The past five years have an odyssey of discovering just how entangled the UK has become with the EU. The first year after the referendum in particular saw daily examples of Things That Turn Out To Be A Problem. Some of those you know about, like the arrangements for the Irish dimension, but others might have passed you by, like pallets or the absence of any legal framework for a British fisheries policy right now.

Even now, Trade Twitter is still working through all the ins-and-outs of what you can and can’t do with a free trade agreement, and likely will be for the foreseeable future.

Thus, we might usefully keep in mind that this is very much a case of a complicated solution not having a simple answer. This is not simply about the disconnect of political rhetoric and substantive regulations, but also about the willingness of politicians to involve and explain such things to publics.

And this is the second lesson: Brexit will be about managing costs.

However Article 50 was to end, there would be costs, be they economic, political, social or reputational. One of the most disappointing aspects of the process to date (for me) has been the unwillingness of any party to explain that to voters.

Leaving with a deal avoids the worst of those costs, but still means reduced economic integration with the UK’s largest market, reduced political influence with both the EU and beyond and the potential for raised social and cultural tensions. Yes, there will be benefits too, but the abject failure to engage with both sides of the ledger has already caused much difficulty, and will continue to do so, so long as this attitude continues.

This is not simply a question of process, but of legitimacy and resilience: already we see how many have become disillusioned by the process to date because the things they were told turned out to be only half the picture, or straight-out lies.

This would be a good point at which to introduce a third observation: Brexit isn’t just about the UK.

The chronic failure of the British political and public debate to recognise that the EU has both a view and a say on UK-EU relations has caused no end of difficulties.

Both May and Johnson have tried to keep the EU at arm’s length from that debate, but both have found that this makes concluding agreements all the harder, not least because the EU’s decision to be very open about its workings exposes any effort by the UK government to wriggle around things.

This will become only more important as we move to post-membership talks, with the EU shifting to a unanimity decision-making model.

And this is the fourth point: The UK isn’t a member state.

Part of the problem of the Article 50 phase was the view in London that this was just like previous negotiations the UK had undertaken as a member of the EU: yes, there’d be tough talks, but ultimately there was an understanding that the club looks after its own.

And it has: it’s just that it doesn’t see the UK as one of that number.

The EU’s approach to third countries has been long-clear: a very uncompromising approach to negotiations, no opening-up of decision-making and no concessions on policy. In essence, third states have to cleave to the EU for whatever they might want.

In this case, the UK has now extracted whatever concessions it might have from the EU – most obviously on Northern Ireland – and it shouldn’t approach the next stage thinking that this will be happening again.

Finally, we’ll come back to another hardy perennial of mine: it’s very hard to negotiate when you don’t know what you want.

Negotiation isn’t easy, but it’s also not that hard: the basics could be grasped very quickly. And at the core of it all is the notion that you have to know what you want.

The UK has lots of ideas about what it wants, but no consensus and – until last Thursday – no means of imposing a consensus.

Perhaps the new government will no be able to do what it wants, but so far the signs are that it doesn’t have a fixed objective in mind, beyond ‘getting it done’; certainly, the priority appears to be about speed rather than substance.

Lacking a strategic objective means it’s that much harder for negotiators to work up a text, for legislators to know whether it’s any good, and for the public to know whether their needs are being served.

Brexit remains the single most important part of this new government’s work and will shape the UK for decades to come: perhaps if we took some time now to reflect on the lessons so far, we might be better placed to make the most of what is to come.