The One Where the Writer Sucked · 9:43pm Oct 17th, 2015
Oh wait, that's most of them...
In S1E20 “Green Isn't Your Color”, it is established that nopony keeps secrets better than Pinkie Pie. Keeping secrets and not being fazed by them is part of who Pinkie is. It stems from an ability to see life as it is and not demand it to conform to her paradigm. This is why she is not afraid of the unknown.