Lefts are a result of the clubface closed when the ball leaves it (seperation). Generally, it is the result of an over-roll or a breakdown of the left wrist through impact.
The following is a post from Yoda, holenone, (I hope he doesn't mind me posting his golden nuggets)that has helped me eliminated the lefts:
Your Left Wrist is Bending during Release and Impact because your Right Wrist is Flattening. And your Right Wrist is Flattening because during (or after) the Release of the Left Wristcock, you are incorrectly attempting to continue that Wrist Uncocking Feel instead of correctly Rolling the Hands.
After the Left Wrist has moved from Cocked to Level -- it is never Fully Uncocked (the Full Extension of the Primary Lever Assembly that results in Zero #3 Accumulator) until after Impact -- the Overtaking (of the Hands by the Clubhead) is accomplished by the Roll of the #3 Accumulator to the end of the Follow-Through. If this correct action is replaced by 'False Feel' Wrist Action -- misapplied #3 Pressure Point Pressure causing a Horizontal Motion in the Right Wrist -- the inevitable result is a Bent Left Wrist and Throwaway.
So, to cure your Bent Left Wrist, you must learn to complete the Release -- Sequenced or Simultaneus (2-P) -- by the proper Left Wrist Action into Impact and Left Hand Hinge Motion into the Follow-Through. But learning these Mechanics is not enough. For total victory, you must overcome the First Snare -- the urge to Steer (3-F-7-A) -- and this requires learning to drive the Ball into the ground and not into the air or 'toward the Target' (6-E-2).
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Yoda, Holenone
It does get much better than that!