Why does Siddhartha consider suicide to be "the most foolish one of all thoughts"?

Death? Not a big deal, says Siddhartha. The novel portrays death as ultimately insignificant – enlightenment is much more important. We see Siddhartha abuses his body in an effort to attain enlightenment, and later, when he doesn’t attain it, he thinks some extremely suicidal thoughts. In contrast, Kamala dies peacefully after having achieved spiritual understanding.