Richard Feynman uses the following figure in Chapter 4.2 of his lectures:
Then he goes on to explain why $W$ must weigh 3/5 of a pound for the system to be in balance. There are two explanations and I understand them both. The first applies the principle of conversation of energy, so if between states (a) and (b) the top weight moved 3 distance units up and the bottom weight moved 5 distance units down, we know that weight $W$ has to equal $3/5 lbs$. The second explanation involves the epitaph of Stevinus, which is even easier to visualise.
Fine, but I'm a noob and there's something I don't understand. Why does the system have to be in balance? Wouldn't the top weight be in the exact same position if we increased the weight of $W$? In my mind, I picture this as the top weight colliding with the pulley and stopping there.
I reckon that there should be a threshold above which the rope breaks, but let's suppose that we increase the weight of $W$ just a little bit.