Optimism is useful because it can help bring more intent to achieving goals. It is harmful because it creates expectations that are likely to be false. Pessimism is useful because if you under-anticipate something, the outcome is likely to make you happier. Hopeless Optimism is an attempt at getting the best of both worlds, i.e. it is a justification of optimism as a pessimist.
If you are hopeless, then you can find acceptance. The degree to which you have acceptance, is the degree to which you have no expectations. No expectations, which results from a feeling of hopelessness, allows you to seamlessly transition from pessimism to optimism. QED