That's what i'd like to know. If you hit the woodwork your attempt at goal hasn't been good enough. Nothing to do with bad luck at all.
It is bad luck. You don't quite catch it as cleanly as you'd like, or you actually catch it too cleanly. There's a slight bobble in the pitch just before you hit it or it hits the wrong lace on your boot. All fine margins that on another day could have resulted in a goal. How many times does the ball end up exactly where you aim for? Not very often. If it's a little further to the right it goes in, if it's a little further to the left it hits the post and stays out. It's bad luck if it's the latter.
Unless we're talking about our home games against (for example) Burton & Millwall when there were quite a number of our fans were quick to claim we were lucky to win both games. Barnsley can be accused of being lucky, but woe betide anyone who claims we've been unlucky. According to some on here, luck only exists when Barnsley gain any benefit, never the other way round.