Why we have phobias and manias

Dear student,
Please find below the answer:

Phobias are developed in any person due to a negative experience or learned response with that object or situation in their early life. Any changes in the functioning of the brain may also lead to the development of phobias. 

Manias, on the other hand, are described as a medical condition that is characterised by signs like elevated or irritable mood, intense energy, exaggerated behaviour, etc. This may be caused by stress, changes in sleep patterns, use of drugs, etc. 

Hope this clears your doubt.
Regards.