Why do I suck at poker?

[navuta]

You only called 1 all in with JJ. The rockets came in behind you. It would have been a bad play if you were last to act, it's just bad luck in middle though.

U are right...
Im reading a poker book.
The little green book, and at some stage it says something like this:
All-in pre-flop.

...Under the following circumstances, I dont think its ever wrong to push all-in.
..
..
..
"I have the worst hand, but even if my opponent calls my all-in bet, I'll be getting the right pot odds."
..

I Dont undestand this sentense. How can someone have the right odds having the worst hand? can someone please explain it to me?
thanks!