Protocols depend on tacit knowledge.

Protocols here could be APIs, or other formal agreements, like laws and contracts.

If you have only the explicit protocol but not the necessary tacit knowledge, you might not be able to use it effectively.

Sometimes the necessary tacit knowledge is minor. Sometimes it is major.

The tacit knowledge is often passed down culturally, or through apprenticeship.

Even seemingly structured protocols can require tacit knowledge.

E.g. SMTP has been around for decades, but to actually effectively deploy it requires you to know all of the little idioms and oddities of real use.

Sometimes you can make hidden tacit knowledge more explicit.

For example, Ian Hickson cleaned up the arcane / under-specified HTML parsing specs a decade ago.

He did it not by actually cleaning up the semantics, but rather documenting, in excruciating, concrete detail, how things actually worked.

This converted previously tacit knowledge into a formal protocol.

However, often the tacit knowledge cannot be made explicit, or the whole thing shatters.

This can happen for example with convenient social fictions that lubricate day-to-day social interactions.