Well, it could be influenced by past experiences, criticism from others, or even the unrealistic standards set by society. 

It often starts with past experiences, especially those from childhood or adolescence. If you had critical parents, teachers, or peers or experienced traumatic events, these memories can leave lasting impressions on how you perceive yourself.

The constant negativity can result in a negative self-image and lead to self-critical thoughts that persist into adulthood.

Unrealistic beauty standards, societal expectations of success, and the pressure to fit in can fuel negative self-talk. 

The media bombards us with images of perfection, and this constant comparison to an idealized standard can make us feel inadequate, triggering thoughts of not being good enough.

Moreover, perfectionism can also contribute to negative self-talk. 

Setting impossibly high standards for ourselves leads to a constant fear of making mistakes or falling short. To protect ourselves from perceived failure, we resort to negative self-talk as a way to prepare for the worst.

The fear of rejection or disapproval from others can also generate negative self-talk. We might preemptively criticize ourselves to avoid potential criticism from others. This fear of rejection further fuels our self-critical thoughts.

During times of stress, anxiety, or depression, negative emotions can amplify self-critical thoughts, creating a cycle that feeds into itself. 

The more negative thoughts we have, the worse we feel emotionally, leading to more negative thoughts.

Ultimately, a lack of self-compassion plays a crucial role in negative self-talk. When we’re overly hard on ourselves and lack understanding of our mistakes or shortcomings, we become more prone to negative self-talk.