This is the only rule that can be broken.
You must tell everyone you can that you have lost.
It is possible to explain The Game to someone without realising that you have lost. Whether this counts as cheating or not depends on your interpretation of Rule 2.
Variations:
Upon loss you must explain the rules of The Game to anyone who is unaware of them.
A warning is required before explaining The Game to others.
Every loss must be announced to at least one person.
