Perhaps it works similarly to a station in a Heroquest, where the Cult knows that a particular statement at that point will get a particular response from the God.
Some gifts have been requested many times and the station at that point is well mapped out. Every cult temple or shrine knows that if you ask for (and I've forgotten the cool name ST gives it) the +5 to Close Combat (Sword and Shield), your Geas will be to never use a particular non-cult weapon. Hence, when you are trained and taught for your initiation, the priest will be strongly advising you to go with what's well known.
The danger starts when you ask for a gift that the temple hasn't tried before. It's like experimental heroquesting - nobody know what will comes out. Sure, nobody is stopping you asking for a gift of +20 to your close combat, but the problem is that nobody around here knows what the geas will be. Risky stuff and the experienced cult members will be strongly advising you to go with the straight and narrow.
It also allows particular priests and temples to know extra gifts and their geases, simply because somebody somewhere tried it in the past.
Harry.
Powered by hypermail