This report delves into behavioral finance, focusing on the influence of psychological biases, particularly greed and fear, on investment decision-making within the UK financial market. The study explores various psychological biases, including regret aversion, herd instinct, overconfidence, and representativeness, and their impact on investors' behaviors. The research incorporates a theoretical model and hypotheses, supported by reliability statistics and ANOVA analysis. The methodology includes a review of literature, the development of theoretical models, and a quantitative analysis using questionnaires distributed to stock brokers at AJ Bell. The report also examines common myths in the stock market and their relationship to psychological biases. The conclusion highlights the significant impact of these biases on investment decisions and suggests strategies to mitigate their negative effects, ultimately improving investment outcomes and reducing market volatility.