If three people jointly own a boat, they might agree that selling it requires all three to accept the sale. Unanimity protects each owner from being carried along by the other two. A single refusal can stop the proposal, which gives even the least powerful participant meaningful bargaining power.
Unanimity is a decision rule, not a promise of warmth or enthusiasm. Some systems require an affirmative vote from everyone; others permit abstention while treating an opposing vote as decisive. In the Council of the European Union's unanimity procedure, abstention does not itself prevent adoption. A private group needs its own explicit definition.
Every refusal changes the negotiation
The possibility of a veto can motivate careful listening long before the final decision. It can also reward someone willing to hold out for a personal advantage. When delay is costly, the most stubborn person may gain influence disproportionate to their stake.
The boat owners would benefit from agreeing beforehand what happens if agreement fails: retaining the boat, seeking mediation, or allowing an owner to exit under a separate arrangement. Without an alternative, unanimity can trap people in a relationship they no longer want. It is especially consequential when applied to routine work: a safeguard appropriate for selling a shared asset can make everyday maintenance needlessly difficult.