How all occasions do inform against me.

From Gaudy Night by Dorothy L. Sayers.  Page 46.

“How all occasions do inform against me!” muttered Harriet to herself. 

This is one of the many occasions where I struggle to keep up with the frequent throwaway lines which are clearly assumed to be widely understood by the reader.  

Definitely Shakespeare.  Maybe Hamlet?  

Yes, Hamlet.  Act IV, Scene IV

How all occasions do inform against me, 

And spur my dull revenge! What is a man, 

If his chief good and market of his time 

Be but to sleep and feed? a beast, no more. 

Sure, he that made us with such large discourse, 

Looking before and after, gave us not 

That capability and god-like reason 

To fust in us unused. 

To accuse especially as a catalyst to an undesired action.