The keeping of secrets and mysteries can give things power, varying by the nature of the secret. There are many ways to accomplish this:

Terms - Secret (an answer no one knows the question to); Mystery (a question no one knows the answer to)

Secret-keeping
One who keeps a secret that literally no one else has gains strength from that secret, granting them the ability to hide things relating to that secret.

Arcane Revelation
The unlocking of mysteries or secrets unlocks the powers of those mysteries. This gives one the ability to find what is missing.

Arcane Initiation
Secret societies create rituals of initiation in order preserve their secrets. These rituals make it harder for disloyal members to break their oaths.

Shrouding
One who knows of many mysteries gains insights into how mysteries work. If one knows enough mysteries, they can tap into them by esoteric weaving arts, making themselves harder to see while wearing these special cloths. Hence the phrase "shrouded in mystery."

Arcane Empowerment
Secret societies can, through ceremonial indoctrination, bind their members together and grant them powers based on how many secrets they share. This can create intricate hierarchies. For instance, the Order of St. Theresa has one hundred special secrets. The first 51 are given away cheaply to non-members, helping them track those who know them. The 49th may only be told to acolytes. The 48th to the next rank up, and so on, until the 1st secret, which is only known by St. Theresa herself. This gives her incredible power over the organization, including the power to control who knows and does not know a secret that she knows.

Secret-binding
The art of binding a secret to a place or object involves whispering that secret to the place or object every night at 3 a.m., then walking backward around the spot or object 7 times. This ancient Tradition leaves a resonance of the secret on the place or object.

Arcane sense
Also called "the detective's bump," this sense is the ability to tell when something is being hidden. Many have this naturally as a weak subset of their "Read People" score, but some develop it through exploring mysteries for long periods of time. Some supernaturally develop it through use of arcane empowerment, secret-binding, or other powers.

Viewing the Unknown
That which is unknown has great power, and those who seek to view the metaphysical essence of the Unknown risk erasing themselves from existence. Those who survive, though, gain enormous power, innate abilities over the mysteries and secrets of the world. In order to view the Unknown, one must close off all of their senses and focus on some profound mystery for three days and four nights, with no rest or sustenance or any sort of break, while sitting in a secluded spot and wearing a white rose. Not even St. Theresa has done this... yet.

Runner Sign
Special graffiti created by Runner 0 that is secret-bound. The language created is complex and supported by subconscious understanding caused by joining the secret society of the Runners, which is unique amongst secret societies in that it has open membership.

Whispering
The ability to spread a secret over great distances, whispering is fueled by the need to tell someone a secret. This happens when a secret's time of revelation has come, objectively and narratively, and it cannot be stopped or controlled.

Questions
An ancient game of back and forth questioning that empowers the initiator by giving them building insight into their partner.

The Lost
Metaphysical questions unanswerable by any (even the Divine), these mysteries are focuses of meditation by arcanists. Meditation upon the Lost can lead to powerful insights into the world and temporary arcane powers.

Deletion
The power to alter the narrative of existence so as to erase parts of it is only available to the most powerful of arcanists, and only attainable by giving up part of one's Name to the Unknown.