Does it actually help?

Yes. One option is to use it as a memorable trigger- "Oh, I'm making mistake X, like the proverb"- and then amend behavior. (This is one of the reasons why it's worth trying to word proverbs as memorably as possible- rhyming helps quite a bit. If your actions you want to jigger, then do not fail to set a trigger! Sometimes it works better than others.)

A superior option is, upon seeing the maxim, to contemplate it fully, and plan out now how it could be avoided in some way, and then practice that offline.

In general, though, de Montaigne is highlighting the general thrust of Less Wrong. Knowing the ways in which people in general make mistakes is most useful to you if you use that knowledge to prevent yourself from making that mistake, and a general mistake people make is to not do that!