Dear Electriccharge,
Every atom tries to stabilise itself to attain a low energy level. The answer to it is hidden in the meaning of stable.It means Resistant to change of position or condition; not easily moved or disturbed. So this is the reason for it to be stable.
It is a fundamental law of Science and life That everything wants to become stable.
Understand by this example:
Now suppose u are a respected man in the society. One day u commited a crime or did a bad work.And from that day onwards all the society members and the people u know started criticizing and mocking at you.That day u lost all the reputation and respect in the society.Then you will start defending yourself and wiil not lose an opportunity or try to do something that you will gain all the lost reputation and respect.Why? Just to become stable and then only you will be able to do your work properly.You will do a good work too to remove the disrespect from yourself . Thats why each and everything wants to become stable.
Now you will ask that the case above was of human beings or living beings.
The answer to that is that we contain a form of energy which we call Biological energy which cannot be defined which we utilise to carry out some work or task and in the same way the non living things also contain some kind of energy for eg; nuclear energy or some any other kind of energy which they utilise to do their work.for eg; All the planets and the Stars and the heavenly bodies which revolve and rotate.
Thats why each one in the universe wants to become stable.
Note :  All that i wrote is my point of view and my logic it may be it can be non applicable but if you understood this and got your answer from this,then its good or you can also find the answer ur self just thinking about it few minutes.
Thank you
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