Found this from a forum:
However, if the trigger is not "generally detrimental", the Judge cannot and will not intervene. It is the player's responsibility to remember his or her own triggers. If that player remembers later, tough luck. But if that player's opponent notices within a turn, that player will have the option of calling a Judge in order to have that trigger go off on the spot. They may also choose not to notify a Judge, and let the trigger pass away.
NOTE, however, that it is illegal for a player to "forget" their own mandatory triggers. It is completely legal for them to since…