Mars in the 12th House
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  You are quite secretive and tend to act for the benefit of others in unrecognized 
  ways. In the twelfth house your natural aggression may be concealed by a vague 
  dissatisfaction with life, but nonetheless, it is one to which you may be resigned. 
  Something is wrong, but you are not quite certain what it is. Perhaps you are inclined 
  to sulk and complain about everything. If you refuse to take constructive action, you 
  will remain dissatisfied. However, once you manage to make somebody else 
  express your frustration for you, it is possible that it will then disappear. Your 
  dreams are vivid, so you would benefit greatly by investigating and interpreting 
  them, clearing up a number of hidden problems.  
   
  With the planet Mars in the twelfth house, you must constantly reaffirm your authority 
  and your personality. Strangely enough, you sometimes achieve this by 
  subordinating yourself to another person or idea. You are able to replace the 
  egocentricity normally associated with this planet through altruism and a willingness 
  to help. The problem with Mars in the twelfth house is not so much that you lack a 
  fighting spirit, but that you may channel your energies in the wrong direction. Much of 
  this is due to the way in which your energy can build up in the psyche but fail to find 
  an adequate outer expression.