Teeqoz on 01 September 2016
If you are an optimist, you are likely to feel like you are succesful, because you won't be thinking about all the things in life that you have been unsuccesful with. And there will be a lot of those things, regardless of if you're an optimist or a pessimist.
Even if a pessimist achieves more on average, they are likely less satisfied with the result, so it depends on what you consider as "successful". Surely if you are satisfied and happy with what you have achieved, you are successful in the sense that matters, right?
