I understand that when a human experiences some aspect of the GodMachine or encounters Aether or Essence they may become a Stigmatic. However, is there an explicit mechanic for this chance based on the character's traits or the nature of their experience to quantify this chance?
I cannot seem to find any explicit mechanic for this, probably because this is more meant as a narrative hook than an actual mechanic. And thus meant to be "up to the GM" to decide if a character becomes stigmatic or not.
As a house rule one could look at skills or traits that deal with the occult, and argue that some trait or feats makes it easier for an invidual to become stigmatic.