I think that Charles (via Lucy) was trying to say that you cannot truly be happy without experiencing the entire range of human emotion. For instance, Linus may be living superficially, not examining his entire experience, existing in a state of denial. Which we know to be true, as he has to put up with Lucy, therefore, should not be happy 24x7 …rofl.
Why don’t they understand that right? It’s not just the look it’s the voice, and of course, the mustache.