The 3D6 Seven, Nine, Eleven, Thirteen, Fifteen Spread

 These are your degree of difficulty, failure, and success array built into the first fantasy roleplaying game, and has been returned to again and again by modern game design to leverage the powerful resolution mechanic it is. 

This is your yes, but; yes, and; no you fucking die "complication" written into this bell-curve and is at least the core mechanic of the Hero System. It is easy to appreciate. Seven thru fifteen is a tight spread you can expect to land somewhere in on an "average" basis, and has enough shade to not seem completely binary. 

Difficulty Class is set on a less swingy basis when using 3D6 than if a D20 is rolled, but still chance rules and there is tension built into each roll, which is routinely exploited at the table for the better enjoyment of all. Coming up with a Difficulty "Class" or Difficulty "#" takes seconds to decide, and with further thought what degrees of success and/or failure  would look like start to paint their way into the picture.