1. The problem statement, all variables and given/known data OK, I've worked up my nerve to ask a stupid question about this problem. I've read the various discussions of it, but I'm clearly missing something. 2. Relevant equations The right-hand mass is 1/(1-t). The sum of the left-hand masses (an infinite series) is also 1/(1-t). 3. The attempt at a solution Therefore, the weight on both sides of the top pulley is equal and a = 0. This clearly is not true, so where did I go wrong? Thanks!