time travel

it seems that whenever someone travels through time in a television show or movie, the moral of their time travels is that the future is not fixed, we make of our lives whatever we want.
on a somewhat related topic, one joke that is popular in movies and t.v. shows these days is to have a character say something like 'i will never in my life step foot on that boat' then the camera cuts to that person stepping onto the boat.
one joke i do like from t.v. is in that documentaries when those dolphins jump through the simpsons chests.