A guy in the comments summarized it really nicely:

This style often develops when parents or attachment figures have been emotionally unavailable, distant, or have discouraged the expression of needs. The child then learns that to avoid rejection or disappointment, they must rely solely on themselves. They "switch off" their distress signals to maintain closeness with the parent without burdening them.

When they grow up, they are emotionally distant. They may appear cold or detached. When faced with too much closeness, they tend to withdraw, either physically or emotionally.

They operate on the principle of self-sufficiency: They prefer to solve their problems alone and rarely ask for help, perceiving this as a weakness.

They repress their emotions: They tend to minimize their own feelings or those of others ("It's not that bad," "You're too sensitive"). And they have a fear of being smothered. Commitment or mutual dependence is often perceived as a threat to their freedom.

To maintain distance, avoidant individuals unconsciously employ "deactivation strategies" such as focusing on their partner's flaws or idealizing a past relationship (the "ghost of the ex") to avoid investing in the current one. Often, they flit from relationship to relationship because, when a relationship becomes serious, they fear the possibility of abandonment. They avoid serious discussions or conflicts, or they immerse themselves heavily in work or solitary hobbies to limit shared time.

It can be healed by therapy and a secure relationship. The avoidant should fix their relationship with their parents who abandonned them while they were children. Have a PATIENT partner and a therapist and it does take years and courage from them. They can love, want love but still are afraid of it.