From Robert Musil’s The Man Without Qualities (part 1, ch.4):
But if there is a sense of reality, and no one will doubt that it has its justification for existing, then there must also be something we can call a sense of possibility.
Whoever has it does not say, for instance: Here this or that has happened, will happen, must happen; but he invents: Here this or that might, could, or ought to happen. If he is told that something is the way it is, he will think: Well, it could probably just as well be otherwise. So the sense of possibility could be defined outright as the ability to conceive of everything there might be just as well, and to attach no more importance to what is than to what is not. The consequences of so creative a disposition can be remarkable, and may, regrettably, often make what people admire seem wrong, and what is taboo permissible, or, also, make both a matter of indifference. Such possibilists are said to inhabit a more delicate medium, a hazy medium of mist, fantasy, daydreams, and the subjunctive mood.
Putting it another and perhaps better way, the man with an ordinary sense of reality is like a fish that nibbles at the hook but is unaware of the line, while the man with that sense of reality which can also be called a sense of possibility trawls a line through the water and has no idea whether there’s any bait on it. His extraordinary indifference to the life snapping at the bait is matched by the risk he runs of doing utterly eccentric things. An impractical man—which he not only seems to be, but really is—will always be unreliable and unpredictable in his dealings with others. He will engage in actions that mean something else to him than to others, but he is at peace with himself about everything as long as he can make it all come together in a fine idea.