What makes you squirm??

I have come to the conclusion that all of us have things that make us squirm. For me well it is plane flights, spiders, and car wrecks. For some of my other friends it is dentist visits, shots and living without her computer.
for another it is birds and letting go of control.
for another it is being alone in her house at night.
Still another is afraid of any sudden sounds you can even tell her you are going to scare her and it still works.

So what is it that makes us squirm with some things and not with others. Like I do not mind shots, birds, or being alone. but why??? life experience? childhood trauma? and how without very expensive therapy so we fix these is there anyone who is not afraid of anything? so tell me what makes you squirm and why??? just wondering.