[runtime_blues]

Early GPTs were fairly bad at following instructions. The innovation was RLHF, where human raters (Mechanical Turk style) would be asked to evaluate on how well the LLM is able to follow instructions stated as a part of the prompt, often in this style. Countless such ratings were incorporated into the training process itself.

So it did not happen out of the blue, and you didn't need a whole lot of existing webpages involving this sort of role play.

[cubefox]

There are two innovations: instruction fine-tuning (via supervised learning), which gives you a model which behaves as if it is in a dialogue (instead of predicting text) and, additionally, reinforcement learning from human feedback, such that it responds to the instructions in a certain way.