Try explaining why tough and rough rhyme but bough doesn't

You know? Language has a ton of idiosyncrasies.

My favorite thing is a "square." I put that name to an enumeration that allows me to compare and contrast things with two different qualities expressed by two extremes.

One such square is "One can (not) do (not do) something." Both "not"'s can be present and absent, just like a truth table.

"One can do something", "one can not do something", "one can do not do something" and, finally, "one can not help but do something."

Why should we use "help but" instead of "do not"?

While this does not preclude one from enumerating possibilities thinking in English, it makes that enumeration harder than it can be in other languages. For example, in Russian the "square" is expressible directly.

Also, "help but" is not shorter than "do not," it is longer. Useful idioms usually expressed in shorter forms, thus, apparently, "one can not help but do something" is considered by Englishmen as not useful.