Loneliness triggers stress and hypervigilance that make us less likely to reach out. Knowing it's wiring is the way out.
The idea
Your body is usually good at fixing what's wrong: hungry, you raid the pantry; infected, your immune system goes to work. You'd expect a lack of connection to nudge you to call a friend. Instead, cortisol rises and you get more stressed, irritable and on edge. For our ancestors, being alone meant being exposed, so the body went on high alert. Polyvagal research backs this up: the nervous system reads social discomfort the way it reads physical danger. The result is a loop: lonely, so on guard, so less likely to reach out, so lonelier.
How to do it
If you feel lonely and also reluctant to call anyone, recognize the reluctance as the spiral.
Expect no help from your nervous system. It works against you here, so the rest of you has to make the call.
Remember that one reason they didn't call you first is that they have the same wiring.
Example
Say it's been a quiet month. An old friend crosses your mind, and right behind the thought come the reasons not to: you're tired, a little irritated, sure they're busy. That's the spiral talking. Make the call anyway; they may be waiting on you for the same reason.