OK, let's say I'm playing a character under that same Belief, "I will bring Joachim's blood to my master".
Am I, in BW, allowed to do some in-character prep around this belief, before the opportunity to gather the blood manifests?
If no, why the bleep not?
If yes, I'd make very sure that after acquiring this Belief my character was carrying at all times a belt pouch containing a stoppered empty vial, an absorbent cloth or sponge, and a knife or scalpel, such that if-when the opportunity ever arises to gather some of that blood I'm good and ready to do so.
As player, I would hope that prep would have, in this scenario, eliminated the need for me to roll anything: the blood's right there, all I have to do is pull out the gear I already have (and I don't even need the knife!), sponge some blood up, and squeeze the cloth so some blood drips into the vial.