Oh, finally found it! It turns out that the tumbler can't fall, on the one hand, because its structure is light on the top and heavy on the bottom, and there is a heavy object at the bottom, so its center of gravity is very low. On the other hand, the bottom of a large flat-bottomed cup is big and smooth. When it leans to one side, its center of gravity and the contact point of the desktop are not on the same vertical line, and gravity makes it swing. If the tumbler falls to the left, the center of gravity and gravity line are on the right side of the contact point. Under the action of gravity, the tumbler will fall to the right. The bigger the tumbler leans, the more weight he loses. When the kinetic energy and potential energy drop to zero, the gravity line just passes through the contact point and will not continue to swing.

It turns out that this little thing, the tumbler, hides a big truth. It seems that everything in life has a reason. If you study it, you will know the truth and make new discoveries.