A right handed shooter will pull shots left when he gets tired and is not pulling into the back wall....a lefty is the opposite. Learned this last weekend at a shoot and it's true...so when you are fatigued you will pull your shots left.
Also, like was mentioned different lighting will cause you to see (use) your sight pins differently and you can get a wandering POI due to lighting changes. Really notice this shooting indoors at different venues.
Again as was mentioned string stretch when shooting under hot conditions is a real effect...a buddy had this issue last weekend at a shoot, his anchor slightly changed and the draw length was longer in the heat.
LC
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