Why is having a sense of humor seen as important? What's wrong with taking everything seriously?
I don't mean not having a sense of humor as in not ever laughing at things which have the express purpose of being funny - e.g. comedians and comedic TV programs - but rather in everyday life.
I mean being sober, sombre, stoical, and taking everything seriously - which doesn't necessarily mean that one is negative or complains often. One can be serious and stoical and still be positive and optimistic at the same time.