Any line segment can be divided continuously ad infinitum. At all times, with each division, the length of each part shortens by a half, while at the same time, the number of parts multiplies by two. So, how can an infinite number of parts, no matter how small they are, make up a finite whole? Because for every division, not just some but all, the lengths of the parts are reducing as fast as the number of parts are increasing.  This means that even as the number of divisions tends to infinity, the corresponding halving of each part keeps the original line segment's length intact.