system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How and why people develop irrational fears and phobias?

There are many people among us with Irrational fears, like fear of spiders "Arachnophobia" (Not like normal fear which is common but really exaggerates one, people that can literally fade if they see one) 
or fear from the ocean, or Ancraophobia or Anemophobia Both terms are used to define the fear of wind, I'm sure there is many more examples.

So how this is happen and why??
gpt
Phobias are the typical example of the manner in which the brain exhibits a One Time Learning or a Single Type Generalisation. Usually, it takes a minimum of 3 experiences to generalise for the brain to learn.
Fear is something which is essential for survival. Fear protects us. However, with fear, the brain responds contextually. For example, if you burn your hand by touching a hot stove, the next time you're going to be careful about it. This is because your brain learns that a hot stove is going to burn you. At the same time your brain also knows that it is safe to go near a stove as long as you don't touch it. Further, your brain may also learn that it is also safe to test touching the stove really quickly, to check whether it is hot or not - and if it is not hot, then it's perfectly safe to touch the stove.
Now, if your brain has an overwhelmingly strong response to the first time you touch a hot stove - either because you burnt yourself so extremely badly that you had to undergo tremendous trauma and stress or because you were punished by someone so severely that you underwent extreme trauma or stress, the chances are that in future, every time you see a stove your brain begins to undergo the same trauma and stress, resulting in a phobia. Your brain is no longer in a position to contextualize the learning.
In extreme phobic cases, just looking at a photo of the stove may result in the phobic response.