Jenga, it's the classic block-stacking, stack-crashing game that everyone played as a kid. You and the person you played with, stacked up pieces of block into a sturdy structure and then you remove these blocks from the bottom or middle and placed them on the top. As you removed a block from the structure you had to be careful of how you removed it because one wrong twist or turn, you could collapse the structure and lose. The reason why it's so hard to remove the block from the structure because there is a friction on the block that resists you from pulling the block fast and smoothly. If the block isn't removed smoothly then the structure will collapse. The reason why this game works and why the structure stays in place when you remove blocks is because of the center of mass of the structure. Even if you take a block from the middle of the structure, this doesn't affect the structure to fall down immediately because the center of mass doesn't move when move the block. It stays constant and keeps the structure from falling. Since the center of mass of the structure doesn't move, the only time it falls is when a block is removed that makes the structure unbalance and fall over.