It’s based on a lot of reading around and experience. For example, I’ve come across a number of people who learnt to skate incredibly rapidly. I got to chatting to them all, and in every case their background explained it. One was a professional dancer. Another had boxed at a high level. Another was a black belt in martial arts. Another had skied for many years. A good example from a book is the case of Kenyan long distance runners who dominated in competition. Someone researched this and discovered they all came from one area where from a young age they ran long distances. Their culture had trained their bodies to excel. When you research successful people, you usually find an early obsession, or opportunities. If someone comes from a family of musicians, they’ll pick it up naturally, they will have ‘talent’. teachers will see ‘talent’ and give them extra encouragement and teaching. Matthew Syed was Britain’s top table tennis player. Most of our best players including Syed came from one street. Turns out they all had access to a table, allowing them to practice huge amounts.
Obviously you need the right physique for a sport e.g. fast twitch muscles for sprinting, tall for basketball. And you need a decent IQ to do well in academic scientific research.
However, everyone I have met believes that talent exists, that some people have it, some don’t. I won’t change anyone’s mind here, and anyway this is well off topic.
I recommend Mindset by Carol Dweck and books by Matthew Syed.