From a scientific point of view, optimism and pessimism are alike objectionable: optimism assumes, or attempts to prove, that the universe exists to please us, and pessimism that it exists to displease us. Scientifically, there is no evidence that it is concerned with us either one way or the other. The belief in either pessimism or optimism is a matter of temperament, not of reason, but the optimistic temperament has been much commoner among Western philosophers. A representative of the opposite party is therefore likely to be useful in bringing forward considerations which would otherwise be overlooked.
(Bertrand Russell, A History of Western Philosophy)