Although numerous theoretical traditions postulate that human fairness depends on the ratio of costs-to-benefits, theory and empirical data remain divided on the direction of the effect. Particularly, answers to the following questions have remained unclear: how cost/benefit ratios affect people’s fairness decision-making during resource allocations, how cost/benefit ratios affect people’s emotions and cognition when they receive fair or unfair treatments, whether people are intuitively selfish or fair, and how cost/benefit ratios of sharing affect it. To address these questions, I conducted three lines of studies in Chapters 2 to 4 of this dissertation. In Chapter 2, I examined how cost/benefit ratios of sharing affect people to make fair or unfair decisions in resource allocations. Results showed that more participants acted fairly when the costs were equal to the benefits as compared to when the costs were higher or lower than the benefits. Shifting from resource dividers to receivers, in Chapter 3 I tested people’s emotional responses and cognitive judgements when they receive fair or unfair treatments at different cost/benefit ratios. My findings revealed that people felt more negative under unfair treatments when the costs were equal to the benefits as compared to when the costs were higher or lower than the benefits. Findings from Chapter 2 and 3 suggested an even-split heuristic: When the costs were equal to the benefits and thus the even-split was fair, more people tended to make fair decisions, and people felt more negative about receiving an unfair offer. Building on these findings, Chapter 4 tested the even-split heuristic using a fast-slow dual process framework and proposed the Value-Heuristic Framework. Results in Chapter 4 showed that people took the shortest time to make the even-and-fair decision (i.e., the even-split was also fair). I also found that people took longer to make the even-but-not-fair decision (i.e., giving an even-split, which results in uneven payoffs), and the longest time to make the not-even-but-fair decision (i.e., giving an uneven-split that results in even payoffs). Based upon the overall findings from my three empirical chapters. I formulated a conceptual framework for explaining and predicting people’s fairness decision-making.