I believe that is a commonly-understood rule of thumb (and it is I think accurate!) but I would add from my own experience (and research): if the pain on the outside of the knee, the problem is irritation of the "IT band" due to the feet being forced to rotate "inwards" (left foot forced CW, right foot forced CCW). In my case I am duck-footed, so a straight hips-over-knees-over-ankles-over-balls (of the foot) alignment twists my feet unnaturally (for my skeleton). Aligning my cleats the way my feet want to be causes heelstrike on the cranks. The problem was solved with pedal extenders, to achieve a wider, what's it called, Q-ratio or something. (I suspect an inverse rule of thumb might also apply, if you are pigeon-toed, then a straight cleat alignment might cause pain on the insides of the knees)

Somebody above linked to kneesavers, that is a fully-customizable option you might need to turn to if you have this problem, but I would first try a cheaper option. There's a guy on eBay that sells pedal extenders for $20-something shipped. Just search for "pedal extenders". Only one size, so if that doesn't work for you, you might turn to the higher-priced kneesavers; they offer a lot of sizes and I believe they will custom-make any size you want.

(If your pain is not on the outside of your knees, or if you don't have duck feet, then this advice doesn't help you. Just learn to spin instead of mash as everybody else up there said!)