Personal optimism is required for how we are to live our own lives. When we consider the great commandment this optimism can be extended to our neighbors. This optimism concerns the person’s potential to be influence by the spirit of the lord in some capacity because of His own self-proclaimed love for them.
This is does not mean that we are unwise concerning the negative disposition of some who may find our company. It is does mean that for us we are to not be moved by the negativity and follow the path that God has set for us to follow. This path is marked by serpentine optimism that creates opportunities for others do and learn the right thing.
By extending the optimism to others we are loving them as we love ourselves. The content of the optimism is of course customized to the person or situation.
The Christian with a sour face that lasts too long is not following God. At least not at that moment. The Christian with a sour face and overly negative disposition for their neighbors is not following God.
This optimism need not extend to positions on large complex interactions like national policy. Pessimism regarding the direction of the culture is different than the pessimism about the person in front of you.