In order to sustain a veto, the president needs the support of slightly more than 1/3 of the members of at least one chamber of Congress. We might think abou this using a simple one-dimensional spatial model of the sort used in the simulation in Module 10.
If the "veto pivot" and all of the other members of Congress who are even more sympathetic with the President's position vote with the President to uphold a veto, then the override attempt will not receive enough votes, and the bill will die. One the other hand, if the "veto pivot" votes with the chamber majority, along with all of the other members who are even more supportive of the bill, then there will be enough votes to override the veto.