I've taught a few dozen ropes course leaders over the years. Knots fall out of people's minds surprisingly quickly. It isn't like riding a bike.

If I were to venture a hypothesis, it is because riding a bike really requires "rewiring" inside the brain, as an all-body activity and involving a large amount of muscles and coordinating them. Which also is why it takes a while, unless you already trained to get the required balance control through some other means (the Asian martial arts fantasy movies come to mind, people running over easily rolling tree trunks floating in water - if you can do that you probably need less time to pick up riding a bicycle).

Knots on the other hand probably mostly only use the existing wiring scheme, so unless you have really bad hand/finger coordination you don't need to change how the muscles (of only arm - slightly, hand, fingers) are activated and used.

Purely intellectual knowledge is easily forgotten unless used, but activities that required certain neurons for proprioception and muscle control to find new connections remain much more easily - also takes a lot longer to gain.

Knots are easy to forget unless you actually understand the knot.

For example, I can tie a bowline as well as most bowline-like knots (ex: sheet bend) without a recipe and even come up with variants on the fly, and I don't think I will ever forget that. This is, of course, after tying a lot of bowlines and forgetting recipes dozens of times.

I think that's for your "riding a bike" analogy. Really understanding a knot takes time and effort, but allows you to remember and even improvise. Memorizing a recipe is faster, more efficient, but easier to forget.

Can you name them ?

My dirty dozen-ish: tautline hitch, bowline, square knot, figure eight + variants, fisherman's knot, N half hitches, sheet bend, Zeppelin bend, trucker hitch, Alpine butterfly, hangman knot, and a variant on the shoe knot that doesn't come loose. Can't remember the name but in sure you can find many variants with a search.

Square knot most people already know. Tautline and bowline are the two worth memorizing being able to do soaking wet in the dark.

Personally I rate the figure-8 over the bowline. I think it's a much more versatile family (and much easier to tie and inspect with high confidence soaking wet in the dark).

Good point! I think I mentally chucked it with the square knot under "knots that should already be in most people's inventory" but you are right, that is definitely worth learning, since there are so many useful variants.

So like, 4 essential knots: Figure 8, square knot, bowline, hitch. The map, filter, fold, and reduce of knots, if you will. Most everything else can be composed from those.

Not the parent comment, but you'll get a long way with a figure-8 (both on a working end and on a bight), a clove hitch, and an alpine butterfly. I'm sure others have a couple more favorites.

(this is omitting a few "foundation" knots like the overhand)

Learn a munter hitch, it's extremely versatile and can do everything from securing something, to belaying or rappeling off it (with a locking carabiner). It is an extremely important knot for setting up rescue systems as it can hold a load under tension, yet can be undone and slack added to the system while under complete control.