In a supplier negotiation, the most consequential move may happen before anyone discusses price: finding a credible alternative supplier.
That alternative changes the options available to both sides. It may make a better price possible, but finding and qualifying another supplier costs time, and switching can introduce quality or delivery risk. The leverage comes from changing the shape of the negotiation, not from assuming the alternative is free or guaranteed.
This is the kind of focused action Rumelt describes in Good Strategy/Bad Strategy: find a point where a well-placed effort can make the rest of the work more effective. What response might the current supplier make? What options stay open if talks fail?
Before funding the search, ask what imbalance it addresses and what risks it creates. If the alternative cannot be delivered reliably, the apparent leverage may disappear as soon as the negotiation ends.
Source: Good Strategy/Bad Strategy