DIAGNOSIS: The lid is vacuum-sealed onto the jar. This happens after blending hot liquids or letting a thick blend sit, creating suction that locks the lid in place.
FIX: Run the jar under warm tap water for 30 seconds to warm the plastic and break the seal. Dry it, then grip the jar with one hand and the lid with the other and twist counter-clockwise with firm, steady pressure—don't jerk it. It should release.
IF THAT DIDN'T WORK: The sealing gasket under the lid may be misaligned or swollen. Carefully pry a butter knife or flat-head screwdriver between the lid's edge and the jar's lip to let air in and break the vacuum. Once off, remove the black silicone gasket, clean it, and ensure it's seated correctly in its groove before reattaching the lid.
HEADS UP: Never try to remove the lid by banging the jar or using excessive force on the blade assembly at the bottom—you'll crack the plastic jar. Always release the vacuum first.