Schrödinger’s Advantage is one of the Potential Advantages rules found on B33.
Erwin Rudolf Josef Alexander Schrödinger's Advantage or ERJASA could be an alternate term used for it, for those who have difficulty spelling that surname, as it creates a convenient acronym.
Unlike the other two it gives no benefits at all until paid for (Heir Advantage works at half power and Secret Advantage works at full power)
The benefit it has over those, is while they can only be paid for when the GM determines it is dramatically suitable, SDA allows the player to purchase it whenever they like: basically waiting until it will be most useful for them.
It in a way works like an Unusual Background for gaining access to other advantages, except being one which is TRADED for that advantage (no added price/value once purchased.