Too broad a question to give a blanket answer, but I can offer some specifics for me:
If it's a skill which is related to one I already have, then it's easy as pie. I can "master" it with only a little practice in most cases. Case in point, I worked as an electronics repair technician for a long time, and I repaired TVs, camcorders, VCRs, etc. Then about 12 years ago, I got obsessed with small Diesel engines and I started collecting Toyotas with Diesel engines (VERY rare in the USA). A big problem with those, is the very fine mechanical workings of the Diesel injector pump, and the tractor belt timing, etc. I had no problem at all mastering all the procedures to repair and adjust those, since I was already fine with tiny mechanical timed parts in camcorders. The fundamentals of understanding technical manuals and schematics and exploded-view diagrams, etc., are very similar. So is the use of tiny tools for fine work. I have picked up many, many skills which I can't say I have "mastered" as if to represent them as qualifications for offering as a trade, but I like having at least some good experience in many many fields. In the event I should want to master one of those skills, I am sure I could do it as quickly as most anyone could. My latest thing, is that I was always fascinated with heavy equipment... Since I do have decent mechanical skills, and a good working understanding of physics, I found it very easy to train to operate a 50,000-lb Caterpillar bulldozer
. It's actually a lot of fun!! ! With the economy so bad right now on the construction industry, I bought a Caterpillar 963 track loader (dozer) for a very good price, and can use it on our ranch for many improvements, and then sell it for what I paid or more in a year or 2 when I want to. I had never touched a piece of heavy equipment in my life, but since I have a fairly good understanding of physics, weights & balances and inertia, I simply read the operations manual cover-to-cover, and also completed an online operators qualifications course (3 hours), and I can operate the machine safely and correctly. Obviously I will get better and faster (while keeping safe), the more practice I get on it.
Other skills, such as trying to learn another language, are a little tougher for me. I can do it, but it doesn't just come to me naturally. Maybe the key is that I can learn anything I WANT to learn...
Charles