One word for someone who doesn't care about anything

A pessimist is someone who always considers negative outcomes of a situation, whereas an optimist always considers the positive outcomes. Is there a word for someone who, in any given situation, doesn't care about the outcome at all?

Solution 1:

I can't think of a noun, but you can say "that person is apathetic".

Apathetic at Oxford Dictionaries

adjective showing or feeling no interest, enthusiasm, or concern

Solution 2:

Indifferent
_{http://www.etymonline.com/index.php?term=indifferent}

late 14c., "unbiased," from Old French indifferent "impartial" or directly from Latin indifferentem (nominative indifferens) "not differing, not particular, of not consequence, neither good nor evil," [...] Extended sense of "apathetic" first recorded early 15c.; that of "neither good nor bad" 1530s, on notion of "neither more nor less advantageous."

Solution 3:

This might not be quite what you are looking for, but as an extreme case:

Nihilist.

This stems from following nihilism (adapted from the OED):

Total rejection of prevailing religious beliefs, moral principles, laws, etc., often from a sense of despair and the belief that life is devoid of meaning.

The belief or theory that the world has no real existence; the rejection of all notions of reality.

A nihilist would not care about an outcome because it is entirely meaningless.

The word has some negative connotations from meaning 1 above, which may make it unsuitable for your particular purpose.

Solution 4:

Insouciant

free from concern, worry or anxiety

Unconcerned, undisturbed; carefree and nonchalant

Origin: 1820–30; < French, equivalent to in- in-3 + souciant present participle of soucier to worry < Vulgar Latin *sollicītāre, for Latin sollicitāre to disturb; see solicitous

as suggested in the definitions the other words I would prefer to use are:

nonchalant

unconcerned

All of these words imply a carefree attitude in a good way and lack the negative connotations of having no feeling at all.

Solution 5:

A fatalist. This does not just mean a person who thinks all things are fated; it has a derived meaning: a person with an attitude of indifference to outcome because of such a belief. An optimist hopes for the best; a pessimist fears the worst; a fatalist is resigned to what will be (regardless of hopes and fears). http://www.merriam-webster.com/dictionary/fatalism