Fixation on basically anything besides God himself may get you into trouble.

I have found the fixation on the Duchess by her twin brother both interesting and disturbing. When we look closely at the thoughts or actions that Ferdinand has towards the Duchess, we can clearly see that he desires an incestuous relationship.The scene in which Ferdinand is holding the naked dagger is a somewhat perverse thing. Ferdinand is unable to decide what exactly it is that he wants from her. I compared and contrasted this though with Antonio's fixation of The Duchess and the way he goes about making her out to be a sort of statue or saint...constantly focusing on her and idolizing her.As the play itself serves as a sort of deconstruction of Catholicism, so does the relationship that lies between Ferdinand, The Duchess, and Antonio. Antonio's fixation can be seen as the "worshiping of a saint" or idolatry, while Ferdinand's thoughts or tried actions/gestures serve to destroy this idolatry-like protestant values and actions
at the time.
http://eebo.chadwyck.com/search/full_rec?SOURCE=pgimages.cfg&ACTION=ByID&ID=38159501&FILE=../session/1235755584_23683&SEARCHSCREEN=CITATIONS&VID=29171&PAGENO=135&ZOOM=100&VIEWPORT=&SEARCHCONFIG=var_spell.cfg&DISPLAY=AUTHOR&HIGHLIGHT_KEYWORD=param(HIGHLIGHT_KEYWORD)
Even though this picture is a process of a monke poisoning a King, it is very relate able to the same idea of ridding idols or figured of worship besides God himself from the public eye. The King, his majesty, could have been seen as a similar figure as the Duchess-someone who was idolized and went against the protestant grain.

Author: Foxe, John, 1516-1587.
Title: Actes and monuments of matters most speciall and memorable, happening in the Church Date: 1610 Reel position: STC / 1925:01
Copy from: Henry E. Huntington Library and Art Gallery