I agree with others, balance is needed, but you should always TEND to be optimistic. There is stuff you can do about your situation, then be optimistic about it and do it. You will be naive, and you will have surprises, but you can always keep learning and see the good in every situation, take the best of it. There is stuff you can't control, well, be optimistic about that as well and trust that God will always love you and protect you.