This study explored the influence of personality differences and their impact within coaching and mentoring relationships through the use of the Big Five personality traits: Openness, Conscientiousness, Extraversion, Agreeableness, and Neuroticism. For analysis, online surveys were conducted, and semi-structured interviews were carried out with 100 participants from various industries. Using a mixed-methods approach, levels of data representation and analysis were evaluated using Pearson correlation and multiple regression for the purpose of validation. The study found statistically significant differences in relationships, with personality traits having a profound impact. Openness, conscientiousness, extraversion, and agreeableness had a positive correlation with effectiveness, while the trait neuroticism had a negative impact. The compounded effect explained 68% of the variance in the effectiveness of coaching/mentoring. The findings provided insights into best practices for adding value in coaching and mentoring, with personalized approaches, effective communication, emotional support, trust building, flexibility, and continuous feedback identified as key factors. The findings also offer a comprehensive framework for understanding the relationship between personality differences and how they can enhance coaching and mentoring effectiveness, ultimately improving outcomes in both personal and professional contexts.