What are relevant and irrelevant information in decision making? And why does short-term and long term decision making change this?

Relevant: Expected future costs, expected revenue Irrelevant: Historical costs from the past (May be useful as a predictor) Sunk costs (Ie. historical costs) are costs we have incurred/must incurre in the future (such as a lease). As we can do nothing about them, they are irrelevant. Fixed costs cannot be changed in the short term. Hence, they are irrelevant for short term decision making but relevant long term.