Obsessions: Synopsis and Effects I've been thinking about this topic quite a lot recently. What exactly is obsession ? Is it a good trait indicating perseverance for a goal ? Or is it a sign of a psychological disorder ? Is it a sort of fixation ? Is isolation its main cause ? Also, is there a reason why geniuses are often obsessed with their fields and thus, driven to insanity ?

I think the most famous kinds of obsessions are obsessions with computers, chess, books and maths. However, is there a general theory to define obsession ? Giving examples of obsessions with different fields would clear doubts.
Obsessions are defined as intrusive and recurring thoughts that an individual finds disturbing or uncontrollable, and are not a good thing. 

There is a lay use of the word which means something like "a very strong interest," but it is just that: a perfectly normal if very intense interest, usually with no basis in abnormal psychology.

Note that 'fixation' is an outdated Freudian concept, unless, of course, you're talking about physically fixating your eyes on an object or area of visual space. Obsessions can be in almost any form, but common ones include recurring and distressing curse words, or a desire to perform dangerous or inappropriate acts (such as a spontaneous desire to jump out of a moving car, or to touch a nearby person in an intimate place.) Importantly, these are distressing and uncontrollable--the obsessive person does not desire these thoughts.