complexity and contradiction

[bosun]

Can you explain what the following sentence indicates?

Provine's well-written ,often amusing, and always fascinating book presents laughter in all its complexity and with all its contradictions. 2) he does not try to sell us a one-issue explanation of laughter.

[Tdol]

WEcan laugh nervously when we hear somethingbad, so there are contradictions; we don't only laugh because something is funny.