Speaking of a sport that I enjoy, swimming will definitely be the one worth-mentioning here.
10 years ago when I was in high school, my mom signed me up for a swimming course at a sports center, which really pissed me off since I was not really into water back then. However, I told myself that I would give it a try to please my mother. Then, the purpose of swimming was explained to me that it would save my life some day in the future. To be honest, my mom was right, because it really saved me twice when I was falling into the water while riding a sinking boat. And now, I confidently say that I have mastered swimming and go to the pool twice a week as I love the feeling of swiftly sliding through the water.
Actually, this skill requires little investment, but the most important thing that you need to memorize is that swimming is the combination of frequent practice and bravery. At first, it could be a trouble for many people since they may be afraid of getting into a deeper water body, but when they have overcome their fear, any place with water cannot pose any threat to them. In terms of equipment, as I mentioned before, this kind of skill needs not much equipment except for those protecting your eyes like goggles or ears like earbuds. Perhaps some people may need supporting devices but then they have to leave them aside to truly swim.