Even the most unsuperstitious and least tradition-bound will stoop to observing the custom of "crossing the threshold" after a wedding — that is, one partner carries the other through a doorway to signify a new chapter.
Nowadays, the "threshold" has come to mean the doorway into their hotel room, but those who are going to an actual house should play it safe and treat both the main door and the door to the bedroom as important thresholds to hoist someone over.
This wedding tradition comes down to us from Roman times when observing it indicated that a bride sacrificed her virginity with appropriate reluctance in that she had to be carried to her deflowering, lest she get away if set down.
These days, most people just see the practice as a general luck-bringer, one possibly linked to any number of cautions against tripping over a threshold. By carrying the bride over this barrier, she at least is spared the possibility of tripping and thus triggering this particular brand of ill luck.