I don't think that's the right way to think about infinity. Just because the chances are infinite and you know goals are possible, it does not mean that there will be infinite goals. There are infinite numbers between 4.0 and 6.0 but only one of them is a prime.
The concept holds. Perhaps the example isn't great, I'm not sure - but since when does 'the set of numbers between 4.0 and 6.0' not include the natural number 5?
That's a set of real numbers, and primality is not defined for real numbers, so 5.0 can't be a prime. The whole concept is just not applicable unless were talking about natural numbers, in which case the set is finite.