I have seen people learn this talent from two sources:
1) A deep, abiding conviction that they will get what they want because they always get what they want. 2) A cheerful disregard for other's predictions of failure (or well-founded empirical observation that the project is anything but a success) -- because "you've only failed once you quit".
Type #2 are much easier to have dinner with but I've certainly seen #1 work.
But what if you started optimistic, but after years of dealing with stupid people who can't even write decent emails, your morale has fallen so low you can't stay excited?
Is there any way to recover, short of wiping your memory of the past and starting out innocent and optimistic again?
Or is that part of what makes it an exclusive trait of the successful, because it is very hard to stay optimistic over the long haul, therefore only a handful actually succeed...
Maybe the pharma industry can make "stay optimistic" drugs just for startups...