They heat up to a greater volume than cold egg whites. Use a heavy-duty, freestanding electric mixer. Beating divinity puts a strain on a mixer's motor. Portable mixers and lightweight, freestanding mixers may not have heavy enough motors. Follow the recipe directions carefully.
Timing is important.
Adding the hot syrup too quickly or not beating the candy mixture long enough can cause divinity to fail. Overbeating the divinity will cause it to set up before you can drop it into individual pieces.