Final answer:
The recent increase in panda births has led to optimism as each new cub is vital for the survival of the endangered species.
Step-by-step explanation:
The recent increase in births is the reason for the optimism. The birth of 19 panda cubs in captivity, in the face of the species being endangered and known for reproduction difficulties in captivity, is a significant accomplishment. Given that there are only about 1,600 pandas left on Earth, each new birth is crucial for the species' survival and contributes to a more optimistic outlook on their future. Optimism is a mental attitude characterized by hope and confidence in success and a positive future. Optimists tend to view hardships as learning experiences or temporary setbacks. Even the most miserable day holds the promise for them that "tomorrow will probably be better."