First of all, what is the volume of the glass? How much liquid is actually in the glass? What is the liquid? Start with data, people. Has anyone even verified that it is indeed a liquid in the glass? Geez.
The problem statement is vague, but I sense that both the “optimists” and “pessimists” are looking to maximize liquid volume with respect to the volume of the glass, except the pessimists have a higher target volume.
Has a stakeholder analysis been performed? What is the Voice of the Customer? How much liquid is actually needed?
Couldn’t the glass simply be too big, making an adequate amount of liquid look unsatisfying relative to the glass? Is there focus group data on perceptions of fullness using different glass sizes?
Is this a closed system? Can’t just we get more liquid? Or dump some out? What about evaporation?
Would a full glass be desirable under all user conditions, such as walking and drinking? Under what conditions will the liquid/glass system be used? What slosh tolerance levels are required?
What other factors affect customer satisfaction? Potability, purity, cost, taste, potency, health effects? This can’t be just about volume.
A pessimist sees the glass half empty. An optimist sees the glass half full. The systems consultant sees .5 EP over four months billable utilization.