Why wrap code into 'document ready'

Question

I\'m new to Jquery. See an example at http://w3schools.com/jquery/tryit.asp?filename=tryjquery_hide_p. Here, clicking \'Click Me\' button the text change. My question is why the

Answer 1

If you don't wrap it, it might not find your element. The page needs to be build first, and then you can look for certain elements to add some functions.

So you say "wait for the page to be finished loading, so all elements I want to change are there" before you start adding stuff to them.