[twblalock]

Yes, most people cannot figure that out, but also it would not occur to most people to consider that when opting for a PIN over a password.

[GeorgeDewar]

One could get into a long debate about whether "most" is literally true or not, but I think most of us should be able to agree that at least a significant proportion of people - enough to matter - either won't or can't think of this without some prompting.