The sheer blank wall doesn't care how much time you have. It's just there. Pass-fail. You're not being graded on a curve. Don't have enough time? Too bad.

Yes, the "sheer blank wall" model could lead to gambling on getting a pass.

However, is the "sheer blank wall" model right? I think common sense dictates that there are a range of possible outcomes, of varying desirability. However, I suppose it is not totally impossible that there are a bunch of outcomes, widely regarded as being of very low value, which collectively make up a "fail wall".

The 2008 GLOBAL CATASTROPHIC RISKS SURVEY apparently pegged the risk of hitting such a wall before 2100 as being 5%. Perhaps it can't be completely ruled out.

The "pass-or-fail" mentality could cause serious problems, though, if the exam isn't being graded that way.