What stops you from having a good nights sleep?

Firstly for me a good nights sleep is, 7 hrs uninterrupted kip and waking up feeling fresh.
The problem for me is going to sleep and getting myself off to bed and feeling sleepy.
I put this down to the patterns of behaviour I learnt as a kid, in that I never really liked going to bed as I always thought I was missing out on something so resisted going to bed and sleep.
This is also why I can never sleep on Aeroplanes, Trains or Buses due to the distractions and action going on around me.
I find dozing off to sleep quite tricky unless I am physically knackered which unfortunately isn't always the case from having a desk job. So my mind starts thinking unconsciously about random stuff and issues which are unresolved and therefore worry me.
So I guess I should join a gym, resolve my worries and learn that sleep is valuable.