If you persuade yourself that you can do a certain thing, provided this thing is possible, you will do it, however difficult it may be. If, on the contrary, you imagine that you cannot do the simplest thing in the world, it is impossible for you to do it, and molehills become for you unscalable.
-- Émile Coué
This sounds like extremely naive optimism. A vast majority of games in all team sports, for instance, probably end in one team failing to do a possible thing they thought they could do.
Post quotes.