A common psychological barrier to starting a fitness routine is self-doubt or a lack of confidence. Many individuals may feel intimidated by their current fitness level or compare themselves to others, leading to hesitation in starting or maintaining a workout program. Additionally, fear of failure or embarrassment in a gym setting can further discourage individuals from adopting healthy habits. Overcoming these mental barriers requires a supportive environment, realistic goal-setting, and self-compassion, ultimately fostering a positive mindset towards fitness and overall well-being.