A DateTime and time zone issue that may surprise you
I was working with a third-party API, and had to specify a date range object, with a start and date. The problem was, their server was throwing intermittent exceptions when I passed this date filter object as a parameter, claiming that the start date was after the end date. I checked the data, and I was definitely sending a valid date range.
The answer to the problem turned out to involve a little-known (to me at least) part of DateTime. Not the sort of thing you encounter every day, but worth knowing about for the times when it hits you.