No extra limbs

Think of a game of . The spinner can keep giving new instructions, but your body still has the same four limbs.

Each instruction changes your pose. If your right hand moves to a new circle, its old position is no longer part of the pose.

Now imagine someone asks where your right hand was twelve spins ago. Your current pose may not contain that answer anymore.

The hidden state has the same problem. Every new word rearranges the same fixed list of numbers. The whole pattern can carry several clues together, but it is not a recording of every earlier pattern.

The sentence can keep growing. The hidden state cannot. That fixed-size state is the bottleneck.