Putting a mirror opposite a doorway or hall gives you a bad feeling because it's momentarily disconcerting to see someone coming towards you before you realise it's your own reflection.
Luck is dependent on mood, among other things - luck is just being able to recognise positive opportunities, and being in a negative mood will attune your perception more toward sources of danger.
Not sure if there's anything else in Feng Shui that has 'real' explanations other than this and the stuff about wind and sunlight. Probably worth going over it all to check, though. Even the stuff that has no strict materialist explanation likely ends up conforming to aesthetic/design principles.