We are very good at avoiding situations we don't like. In fact, we can be so good at it, we don't realise we're doing it! Understanding why it happens, and what we can do about it, is a good place to start.
Avoiding the 'bad thing'
Avoidance is a type of coping mechanism - stay away from the 'bad thing' and you don't have to deal with it. But if left unchecked, we can go to greater and greater lengths to avoid feeling fear.
For example, perhaps travelling in a train has made you anxious at some point - you may even have had an anxiety attack - so what, you say to yourself? You take the car most days anyway. But the more you avoid it, the more salient the message you are giving yourself that it must be avoided. "I don't DO trains"
And without facing it, the fear can generalise. The experience of being in a train may have left you feeling anxious, clammy hands, shallow breathing. Not nice. However, you may find yourself in a bus at one point and find it reminds you of being in the train. All the similar elements will be connected with the train...the crowds of people, the sense of being caged in, the fear of panicking in public. Your hands become clammy again and your shallow breating kicks in.
No buses for you either now :)
Making Connections
At a funfair, months later, you suddenly feel an immense unease - too many people - just like the bus. Instantly, your breathing becomes rapid, and you feel the need to 'escape' - with the fear of having a panic attack in a public place looming large.
Phobias can become debilitating, depending on the stimuli, and affecting normal functioning if they generalise to everyday situations. Of course, this may not always happen - perhaps the phobia stimulus is rare enough that it does not need 'avoiding' eg., fear of snakes. (Until you take that dream job in Africa).
How Therapy Can Help
Therapy can provide you with the tools to overcome your phobia, and diminish its effect on your life by developing an awareness of what is going on for you, emotionally, physically and intellectually.
By understanding that you can 'rewire' your neural pathways, you can regain complete control of your reaction to negative stimuli. And if you do land a job in Africa - the snakes are not so bad - it's the spiders you should be wary of...