I'll start, and then I'll turn to my colleagues from the Department of Finance.
The first thing you'll see is departments lapsing. The Department of Finance knows that departments are going to lapse, so they build a lapse factor into their forecast.
I would say that historically, and my friends from the Department of Finance can correct me, government's been pretty good at projecting expenses. Revenue is often the more challenging piece. If you go back to when this discussion started, the reason was different every year.
If you look at where the expenses were different from projections in budget 2015, it was in areas like employment insurance. The economy was not as strong as originally forecast, and we had transfer payments to Alberta and Newfoundland that were related to fiscal stability. Again, those were for unforeseen things. I think that's explainable.
They may wish to comment on my statement about revenues versus expenses and which are tougher to project.