I was going to ask this question after getting some misleading information from my can of poly, other questions and answers here and from my own experience.
What I never understood was why should I not shake the can? The instructions from Minwax's website don't really explain why, but state:
Stir Minwax® Fast-Drying Polyurethane before and during use to eliminate settling on the bottom of the can. Stir in such a manner as to rotate the product from the bottom to the top of the can. NEVER SHAKE
Barring spilling the product all over the place; what am I risking if I shake the can?