Why one token changes the answer

The sentence describes one thing trying to fit inside another. trophy is the thing. suitcase is the container.

If it was too big, then it must be the thing trying to fit. That is the trophy.

If it was too small, then it must be the container that could not hold the thing. That is the suitcase.

The model was not given this exact rule. During training, it learned many language patterns connecting things, containers, size, and fitting. Those learned patterns are stored in the model's weights.

Changing one token changes which relationship fits the sentence. Attention helps the model select the relationship that fits now.