When doing risk planning for your project, don't forget about seemingly off-topic risks, such as the weather, or the season of the year. It's an obvious concern if you're in the construction or farming industry, but in many other organizations, timing your project rollout to avoid quarterly closes, the company's peak season, or any other major seasonal events, can make or break your project.
I've heard of one popular confection organization that couldn't ship candy during Halloween because of a problem with their new SAP implementation. Bad timing. Another company that dealt with agriculture had to have a project completed before the summer growing season. They were smart enough to list that as a constraint.
The seasonal elements didn't just affect Napoleon in his failed Russian campaign (and many before and after him). It can affect those of us in business as well.