Also applys to the decay of physical storage mediums.
Sally "Must be bit rot"
For example, if I've written a patch for Firefox 5 years ago, I won't be able to use it to patch the current version of Firefox.
For non-geeks, compare it to a car. You and me are building a car (big project). I've made an engine (the original patch) but haven't installed it in our car yet because I didn't have the time. While I'm trying to find time to install the engine, you install some bicycle pedals (a conflicting patch). My engine won't fit anymore, it now suffers from bitrot.