This discussion of avalanche effects somewhat contradicts two simplifying descriptions made in previous panels. Details are always messier.

The idea of an avalanche effect is that we would like every bit in a cipher output to depend not just on the key, but also on every bit of the plain text input. Two plain texts that differ by a single bit should nonetheless produce cipher texts with no predictable similarity, even though they will be encrypted with the same key. To accomplish this goal, encryption algorithms need to recruit input bits to serve a key-like role within the algorithm. But each input bit needs to serve this key-like role in a manner that is diffused throughout the entire cipher text, not just in those cipher text bits that are nearby or that have some other simple relation to the key-like input bits.