Originally Posted by
operator
The upper position on the chain tool was designed to resolve stiff links. The other option is to bend the chain with your hands back and forth. Don't do this on 10 speed chains.
Try the bending trick first, that usually gets the milder cases. If not, push the pin ever so slightly with the upper position, but make sure that the pin is still centered and that it sticks out past both plates, otherwise the link could pop apart.
What type of chain is this?