Reply #2: There are dozens of exceptions...

[Davis_X_Machina]

...and they are hard to generalize about.

The rule often is violated when a word comes from the Germanic (Anglo-Saxon) side of the English language family tree -- neighbor, weigh.

It is more likely to be observed when the word comes from the Romance (Latin & French) side of the family tree.

But even then, there are scads of counter-examples -- e.g. friend, which is cognate with German Freund.