As someone on Reddit wisely said, “WD-40 is like duct tape–useful for a lot of things but the worst choice for all of them”. It’s successful because an extremely persistent myth developed that it’s an all-purpose lubricant. WD-40 is **not** a lubricant.
I’m guessing their sales are heavily driven by this misunderstanding, and they’re certainly not going out of their way to correct this. Yes, 10–20% of the ingredients (mineral oil) have some light duty and short-term lubricating qualities, but it can actually remove lubrication because it has some degreasing properties.
I went from using WD-40 for everything to using it…for nothing. There are much better lubricants (e.g., 3-in-1, silicone spray, lithium grease), much better degreasers (e.g., dish soap, Goo Gone, Krud Kutter), and much better penetrating oils to loosen bolts (e.g., Kroil, Liquid Wrench). Any homeowner will be happier with the performance of a product specifically made for the problem they’re trying to solve.
About five or six years ago, I saw a special deal on WD-40. Two cans packaged in shrink wrap for not much more than one can. We used up the first one and we’re about halfway through the second one. I used it this morning to clean and lubricate the rotation joint in the surface cleaner we used to power wash the deck yesterday.

This fall, I’ll use it to clean and lubricate the hose valves that distribute water to our fruit trees, kitchen garden, and flowers.

It’s successful because it does a good job, doesn’t cost much, and it lasts damned near forever. Patents protect the rights of the inventors; in this case, can you imagine someone selling a competing product without comparing it to WD-40?
