Boris Johnson and his scientific advisors presented modelling showing why they believed it was necessary to put England into lockdown - but they did not show anything to explain how we would get out.
This kind of information is crucial because lockdown timetables have a tendency to slip. Indeed, that process may have already begun.
On Saturday night, the prime minister gave a firm deadline for exit: 2 December.
On Sunday, Michael Gove told Sophy Ridge that the government could extend the lockdown if the data shows the infection rate has not fallen far enough.
What are England's chances of making it out on time? The question is as infinitely complex as human behaviour, yet at the same time extremely simple: It depends whether the distance we put between ourselves is enough to overcome the spread of the virus.
In March, the UK delayed lockdown at a point when infections were doubling every 3 or 3.5 days, the R was between 2 and 3 and prevalence was very high. The end result was one of the longest lockdowns in Europe.
Official definitions of lockdown vary wildly from country to country, so we used a comparable measure: The reopening of pools and gyms. By that standard, France's strict, early lockdown lasted 97 days. The UK's ran for 124.
This time, the R is around 1.3 and the doubling time is closer to 14 days, which should make the outbreak easier to suppress. On the other hand, schools, universities and colleges in England will remain open, so the lockdown won't be nearly as strict as before.
The country is facing a smaller problem than it did in March, but bringing less strength.
This picture of competing forces pulling against each other like two teams in a tug-of-war is borne out by the most recent scientific assessment of the impact of lockdowns, a paper by scientists including SAGE member Graham Medley.
Professor Medley and his colleagues considered the impact of a two-week circuit breaker lockdown over the October half term in England, examining a range of more and less restrictive measures, from the total lockdown of early April to the relative freedom of August.
Looking at their forecasts for a 5% growth rate, the current rate in the worst-hit areas in England, two things stand out clearly.
First, even the toughest measures take some time to have an effect. Infections fall quickly after restrictions are brought in, but hospital admissions take at least a week to decline, and deaths take even longer.
It is quite possible that deaths will still be rising in the third week of November. We should prepare ourselves for that eventuality.
Second, no matter what you do, hospital admissions bounce back very quickly once you reopen. In the toughest lockdown modelled by the scientists, with education closed, it took about four weeks. In the second strictest, roughly comparable to the one England is about to undergo, it took about two.
England's lockdown is due to last a month rather than two weeks, so its effect should last longer. But sooner or later the virus will come roaring back. These models show that it will most likely be sooner.
None of this is fixed. If a lockdown produces a lasting change in behaviour its effects can endure long beyond its official end. At the start of October I asked a scientist who advises the Italian government why Italy hadn't seen a resurgence of cases. I expected an answer involving R numbers and heterogeneous mixing factors.
Instead he said: "People were scared. They changed how they behaved. That's really the only answer I have."
For this reason, the communication of this lockdown is a cause for concern. Various reports have billed it as an attempt to save Christmas. While it's entirely understandable, if we get through this lockdown only to rush off to see our families, we will inevitably bring back the virus faster if we do.
It may be a lot to ask, but only this kind of dramatic shift may be enough to prevent lockdown numbers three and even four.