PMI (plus, minus, interesting) is a retrospective activity that encourages participants in a discussion to look at an idea from more than one viewpoint.
Running the activity:
1.       Split the canvas into 3 areas: plus, minus, interesting.
2.       Ask participants to add notes to each area
So, in the context of this retrospective, please share with us what you consider: positive (Plus), negative (Minus), or Interesting. Please write each note on a post-it, and place them on the respective canvas area.
3.       Group conversation about the notes
 
 The PMI thinking activity was developed by Dr. Edward de Bono, the father of lateral thinking and creativity.
I first came across this activity on Margaret Rouse great post on PMI.