Based on my conscience , and using Otto's example:

--I would book Ticket 1 as far in advance as possible, with my conscience telling me that Ticket 1 was all I needed.

--Perhaps a week or two later, I'd suddenly realize that I need to get back to home over the weekend, but my conscience tells me that's a separate issue with a separate ticket purchase. At that point, because my situation has changed, I would book Ticket 2.

QED.