Is there a benefit to telling a kid they can be or do anything they want off of their efforts alone or does it do them a disservice?

Where is the benefit to tell a kid they can be anything they want if they work hard enough? What about those goals or endeavors that take the blessing or involvement of others to complete? If a kid is legally blind and can barely see 4ft in front of them how could they be a NASCAR driver, pilot, champion ping pong player, etc when you need to see well to do those things? If the child has actual physical deficiencies that can not be counterbalanced with simple hard work and effort is that not applying or setting up unrealistic expectations in a child? Would it not be better to give it to them straight that some things are outside of their control and need the participation of others to work?