Good is not different from Bad?

In the book *Zen Mind, Beginner's Mind*, I read the following statement: > This is the basic teaching of Buddhism. Pleasure is not different from difficulty. Good is not different from bad. Bad is good; good is bad. They are two sides of one coin. How does this make sense? Does this mean that every good action (for example trying to reduce suffering) is somehow also bad? Or at least destined to fail?