37. Come On In, and Watch Your Step
This one seems bizarre on the surface, but is, in fact, a very important custom among Buddhists. Were you to ever visit a Buddhist monastery, for example, you would have a similar expectation put on you to not step on the threshold. The reasons for it are varied, but it is an old tradition.
The explanation is the threshold is something of a barrier. One version explains that getting it dirty would harm its ability to keep the building clean and ward away evil. Another possible reason is it is seen as a barrier to the gods and will destroy your feng shui and clash with the family god.