Answered from Before Attention: The bottleneck of a single context vector | The Attention Family, Lecture 2 · The attention family · 2026-09-04
Because an RNN reads tokens in order, information from the start of a long sentence tends to fade by the time the final hidden state is formed, which keeps more of the sentence's end. In Vizuara's example, 'the teacher who was teaching a difficult concept to the students smiled', the word smiled sits right next to students but belongs to teacher at the very start, a link a context-vector model finds hard to keep.
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