What's the secret of the poem in chapter 6 1 of the Water Margin?

It means: adapt to the day when you look for a higher development direction. For your current period, it is an opportunity for upward development. If you can seize any opportunity, you will have a further possibility. The most taboo is the shrinking thought of "I'd rather be the head of a chicken than the tail of a phoenix", which will make you curl up in Xiaotian's own land and unable to go further. Perhaps, you can also talk to an admired elder, and a biography book can play a similar role.