Flares fascinate. How and why do these huge high-temperature events erupt? Close study of the polarity of sunspots suggests they occur along the boundary between spots of opposite sign. At least this GOES M4.2 did in AR12673 two months ago. The sketch (lhs) shows the spot group in WL and H-alpha (polarity line in BLUE). The polarity map from the (c)SDO satellite shows the polarity a few hours later.