that way madness lies

• that way lies madness

From The Tragedy of King Lear (c. 1606), see quotations.

that way madness lies

1. (hyperbolic) The mentioned activity will cause frustration, anger, etc.
   • c. 1603–1606, William Shakespeare, “The Tragedie of King Lear”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, →OCLC, [Act III, scene iv], page 297, column 2:

     Your old kind Father, whoſe franke heart gaue all, / O that way madneſſe lies, let me ſhun that: / No more of that.

   • 1994 September 16, Roger Ebert, “Timecop”, in Chicago Sunday Times‎^[1], archived from the original on 2005-11-13:

     You see what we're up against here. "Timecop," a low-rent "Terminator," is the kind of movie that is best not thought about at all, for that way madness lies.

• Gary Martin (1997–) “That way madness lies”, in The Phrase Finder.