That's bollocks isn't it?
Quite aside from whether or not you like the Shawshank Redemption which this is of course the tagline from, surely it doesn't actually work in practice.
If you're in a crap situation and you have hope it's gonna get better, you tend to sit around relying on that hope and never actually doing anything to improve your life - so hope is in effect keeping you prisoner.
Whereas if you're in a crap situation and you fear you'll always be in that crap situation then you feel motivated to get off your arse and do something to improve your life - so in effect the fear sets you free.
For example if two people were stuck on a desert island, surely the one that's so scared of spending the rest of their lives there that they build a raft to escape has got a better chance of getting away than the one who sits around hoping for a ship?
If anyone thinks I'm wrong on this, I'd be very interested in them explaining the tagline to me.