Why You Think You Can't Learn That (Before You Even Try)

Attaching importance, danger, and anxiety:

Making a big deal out of things is part and parcel to the human ego, so the bigger/more inflated/damaged the ego, the more the person will do it.
Because of this, younger people often get the impression from older people that many things are much, much more difficult to learn or to do than they really are; that certain kinds of people or certain individuals are much more "important" than others, and that methods, ideas, beliefs and stereotypes are absolutes that are engraved in stone. It can also cause dramatic envy issues, where people compete for "importance", attention, credit, and position.

On one hand, a young person can believe that something is too hard for them to learn how to do, or too scary or dangerous to even try. Many around them in such groups will encourage these beliefs, because it keeps that young person as a "less important" person, which means that other people are automatically"more important". On the other hand, another young person can make a goal out of "becoming" one of these "very important people" that do "very important" or "very difficult" things. So in the same family or community, one child may be afraid to even try to learn to play the piano because people are making it out to be such an extremely difficult skill for just an "average person" to learn, and another child will set out to become a Piano Player Person because of the same people painting Piano Players as "Smart/Very Talented/Important People". In the same group, another child will hide their piano-playing ability because people around the child project the assumption onto them that the child is ONLY playing the Piano to get attention and LOOK IMPORTANT.

So one kid is afraid to try to play Piano because people imply that it's so hard (too hard for "normal" people, or for that child), another child is doing it ONLY BECAUSE people imply that only smart or important people can play the Piano, and yet another child is hiding their ability to play because people accuse the child of only doing it to LOOK smart, cool, or important. So the child who ends up getting recognized for playing the piano out of the three of them is not the one with the natural ability, or the one who finds it fascinating, but the one who really is only doing it to get attention. And that's part of the cycle: that child will project his or her own motives onto others in the future, and assume that others with love for music or natural talent are actually only playing music to get attention (like he/she is). The child does not know that everyone's motive for playing music is not the same, and may not ever learn that. So, those who play music with that person in the future will find themselves in an ego/power struggle. If that person becomes a teacher, he or she will compete with his/her own students, and project his/her own motivations onto them. That means the student with a very high natural ability OR fascination for music will be treated by this teacher as if they have an inflated ego and are trying to steal the "spotlight". The student who has an interest in learning piano will need to overcome the projections and implications that it will be "too hard" for them to do; many people don't get over this hurdle. And even if they do get over it at first enough to learn how, they still will have to keep pushing past more projections (you're only doing it for attention/you're not that good/you're not important enough to be a REAL piano player/you think you're better than other people) as time goes on and their ability improves.
If one applies this template to other fields of work and study, one can start to unravel some of the dynamics within.
There are, for example, a lot of carpenters out there who don't actually enjoy woodworking or building, and many who aren't even good at it, but who are only doing it because they were led to believe that it's a "man's" job, and that if you do carpentry, it proves that you are a "man", or "clever", or "important", or "tough". Also because it's an easy way to make money if people believe you can do it.

There is a very big difference between a person who does carpentry because they are fascinated by it and talented at it, and a person who is really doing it because they want others to recognize them as "masculine", "capable", or "important", or just to make money. Like any other field or interest, the person who does it because they're genuinely "into" carpentry does not make a big deal out of how HARD it is or how DANGEROUS it is or how TOUGH a person has to be; they're not focused on OTHER PEOPLE (or their own image), they're focused on the CARPENTRY. But a person who is doing it to "prove" or "show" something is quite focused on other people. If they are trying to show that they're "Masculine" by being a carpenter, then they'll hate it when a woman shows up doing the same job. They may also hate it if a smaller man shows up, or a child, because it would wreck the image altogether of "I can do this because I'm so masculine". Turning carpentry into a BIG DEAL gives the impression that only PEOPLE who are a "Big Deal" would be able to do it. So anyone who's NOT doing it is not a "Big Deal" person, and wouldn't be able to do it even if they tried. A small man, woman, or younger person doing the same job messes that all up, so they are kept out of the field if at all possible by creating a "hostile environment".
ONLY IN DYSFUNCTIONAL GROUPS are "hostile environments" allowed to remain or flourish.

This is not a male-only phenomenon at all, but it does seem to be more prevalent in anything that people try to label as "male", from cooking on the grill to video games to Poker to comic books to Physics. In fact, it seems to work SO well that people will purposely label something "male" just to attach the image so females will hesitate to join or learn, mostly for worry of having to deal with a "hostile environment".
It of course works quite well the other way also; labeling something "female" will cause conditioned boys and men to avoid it so they don't get identified with it by their peers or by older males.

Making things a bigger deal than they are and attaching labels to them keeps people from learning how to do things, from doing certain things, from going out into the world, and from pursuing and expanding their interests. It's a very effective Control tactic.