There is a difference between positive thinking and pure delusion. You can be hopeful and try to work hard in a bad situation and hope that things get better. Positive thinking help people get through bad situations and look forward to tomorrow.
However, if you are being delusional about stuff and pretend the problems just don't exist, that is when things start being a problem.
My way of positive thinking is, "Things are bad right now, I can work hard and make things better."