Are we just really lucky that the time it takes for earth to orbit the sun is 365.25 days? I mean if it was something like 365.71 days, then we couldn't have our simple leap year every four years. We would have to have a 71 leap years every century, or even if we were to simplify it a bit, 7 leap years every decade (with maybe two instead of one the last year). Does that make sense? Is it coincidence, or is there some reason behind this?