I think that some of those who struggle with mental illness like depression are actually some of the more optimistic people out there, oddly enough. It takes a lot of determination and buried optimism to keep going when what you really feel like doing is hanging yourself from the nearest rafter. So while a lot of us have trouble seeing the good in our lives, I think it takes a lot of optimism on a very deep level to keep going anyway.

P...positive emotion (ie optimism)
E..engagement (taking part in society)....
R(relationships)....
M(meaning:do you feel your life has meaning)....
A(accomplishnents)