I have not read this poem. But from this sentence taken out of context, I understand it as follows: Life is like a play, and it cannot be happy all the time. Joy and sorrow are the true meaning of life. Happiness comforts your parents, but sadness makes you grow. Happiness brings you wonderful memories, but sadness makes you gain a lot and understand gains and losses. So the meaning of this sentence may be that we welcome surprises, but we do not reject (or cannot) be sad. In my humble opinion, let’s just throw some bricks and mortar into the conversation.