When people don't post. Plain and simple.

These days, just about every electronic device in the world has internet access, (this is an exaggeration) and there are lots of places that have free Wi-Fi. Even if you are unable to type an RP post, you can still put something quick in the OOC at least to let people know what's going on and/or keep a discussion going. I hate coming on, and seeing nothing going on in the RP's I'm in for days/weeks at a time... :/