Isn't optimism good? Why does Master Shengyuan say excessive optimism can make life harder?

Optimism has advantages, but if it reduces your attention to detail and caution, it can cause unnecessary hardship. I have experienced both sides myself. Retaining strength in difficulty needs to be distinguished from oversimplifying things.

I used to be more easygoing, handling whatever arose rather than imagining the worst from the outset. As a child, I even thought that if the sky fell, someone taller than me would hold it up. This personality really did help me through many setbacks, giving me strength to break through and move forward.

Looking back, though, there were also times when I was too optimistic, failed to think carefully enough or act cautiously enough, and learned what I should have noticed only after making mistakes and suffering setbacks. So when discussing my optimism, I remember the strength it gave me while also acknowledging where I still need adjustment and learning.