When John Stuart Mill said “One person with a belief is equal to ninety-nine who have only interests” he contrasted the power of those with an active conviction on an issue to those that give the issue more passive attention. In essence, beliefs can be used to bring greater rigour to thinking and problem solving. The Thinking Ahead Institute’s long-horizon working group discussed this belief and based on working group discussions and further research proposed nine core long-horizon investing beliefs for investors to consider and adapt. This research paper looks at each belief in detail and how the investment community can adopt them in practice.