Full Idea
The principle of sufficient reason says no fact can be real or existing and no proposition can be true unless there is a sufficient reason why it should be thus and not otherwise, even though in most cases these reasons cannot be known to us.
Gist of Idea
No fact can be real and no proposition true unless there is a Sufficient Reason (even if we can't know it)
Source
Gottfried Leibniz (Monadology [1716], §32)
Book Reference
Leibniz,Gottfried: 'Philosophical Writings', ed/tr. Parkinson,G.H.R. [Dent 1973], p.184
A Reaction
I think of this as my earliest philosophical perception, a childish rebellion against being told that there was 'no reason' for something. My intuition tells me that it is correct, and the foundation of ontology and truth. Don't ask me to justify it!