Exactly. As if voting Leave isn't inherently an enormous gamble based on a particularly ill-informed bout of economic forecasting.
Claiming that we don't literally know exactly what will happen in the future is too obvious to merit restating. But we can make informed assessments based on available evidence. Governments do this, central banks do this, corporations do this, investors do this, and everyday consumers do this. Just like my "Are we going to win the league?" analogy, or Bruce Wayne's weather reports.
If you insist, no, I don't literally know that we are not going to win the league, so to speak. But at this point, Brexit is in akin to betting the house that we will. If you won't consider the clear and abundant indications that this is going to be a very bad thing - to say nothing of the clear and abundant evidence that it is and has already been a bad thing - you're deluding yourself.
The lack of honesty and engagement on behalf of Leave here is quite telling.