Subject: Why are some hard-boiled eggs easier to peel than others?

Often, when I hard-boil eggs, the membrane under the shell is so tough that it 
pulls a great deal of the egg white away with it. I've also noticed that in such 
cases, the egg sems to peel away in layers, much like an onion. I've tried 
different boiling times and freshnesses of eggs, and can't seem to find a 
correlation between eggs that peel the way they're supposed to, and ones that end 
up a lumpy mess with half the egg stuck to the membrane.

Re: Why are some hard-boiled eggs easier to peel than others?