To understand why, it is crucial to remember that Britain’s departure from the EU is not a single act, but a process. While the country is now certain to formally leave on January 31, that is only the first stage of its disentanglement. Once Britain has withdrawn from the EU, it will enter a so-called transition period, in which it will continue to accept all EU rules and regulations in exchange for maintaining the economic status quo until a new trade deal is agreed on. In effect, nothing will change.

Read: This is just the beginning of Brexit

The problem is that the transition period, which runs until the end of 2020, is not long enough for much to be agreed on at all. Basically, unless the United Kingdom requests an extension to this period, something Johnson has categorically said he will not do, both sides have less than a year to agree on a trade deal, avoiding the imposition of tariffs, quotas, checks, and controls. Failure to do so would cause an economic shock to Britain, Europe, and the wider world. Because of the threat of such damage, many analysts believe that Johnson will eventually cave to whatever demands the EU makes, signing on to terms that maintain trade while binding Britain to the EU’s economic and regulatory order.

Those who have been involved in the Brexit negotiations or know Johnson are not convinced by that argument, though. On Brexit, Johnson appears to have one clear guiding principle: sovereignty. Brexit, in Johnson’s view, is fundamentally about self-governance and democratic control—the British government’s ability to do things differently from the EU and to be answerable to the British people for those decisions. He has argued that this, not economic integration, is the foundation on which Western prosperity is built and that, therefore, Brexit, if it is to mean anything, must be about the repatriation of economic self-governance. Were Britain to maintain a tight relationship with the EU, it would then have to sign on to the EU’s standards, and even, perhaps, be subject to European court rulings. One former diplomat who has worked closely with Johnson told me that even when Johnson was Theresa May’s foreign secretary, he would openly declare that the whole point of Brexit was to be able to diverge from Europe.

Read: It’s Boris Johnson’s Britain now

This is a stance on which he has been relatively consistent. As mayor of London, he wrestled with which side to back in the Brexit referendum before plucking for Leave. Why? In the Daily Telegraph column announcing how he would campaign, he claimed that it was because of “the inability of people to kick out, at elections, the men and women who control their lives.” Johnson said then, in early 2016, that Britain had “become so used to Nanny in Brussels that we have become infantilised.” When May proposed a future trading relationship after Brexit that would have seen Britain accept EU regulations without a vote on their adoption, Johnson quit her cabinet. He said at the time that May’s plan was only a "semi-Brexit" that would turn the U.K. into the "status of a colony.” Once he succeeded her, he negotiated a new Brexit deal, stripping out clauses that tied Britain to the EU labor market and the bloc’s environmental standards.