How much do organizations such as Amazon, Facebook, Twitter, Hacker News etc. plan ahead for holidays such as Christmas, Easter, Thanksgiving, Mother's Day, or

How much do organizations such as Amazon, Facebook, Twitter, Hacker News etc. plan ahead for holidays such as Christmas, Easter, Thanksgiving, Mother's Day, or the last day of school, first day of University? It seems most outages could at least be predicted somewhat just by looking at "cultural patterns", for lack of a better phrase, from my perspective a lot of outages seem to occur during the events I mentioned. Add to that most people and resources may not be available as much or as quickly during the days when it's busier making it even more likely something will happen.