The placement of Mercury in Aries indicates you have a need for mental self-assurance. Very often, the tentative mental apparatus that you possess needs to be reinforced by a heavy dose of assertiveness. Much of the behavior and many of the personality characteristics associated with Mercury in Aries are a result of this need to be mentally confident. Being able to turn your thoughts and words into action may also provide self-confidence. 

Mercury is generally well-placed in Aries. Aries is the Cardinal Fire sign. The active fiery nature of Aries symbolically harmonizes well with the quick and airy nature of Mercury. Thus, the Mercury-associated functions are stimulated and activated. There is a danger, however, that Mercury’s mental energy could be overwhelmed by Aries’ need to act, resulting in mental impulsiveness and lack of self-control. This danger is symbolized by the natural quincunx between Aries and Mercury-ruled Virgo. 

Insecurities

With Mercury in Aries, mental insecurity stems from a subconscious realization that the mind is treading on new and uncharted round. It must keep up its confidence despite its lack of experience. This need to keep from giving into insecurity and maintain self-assertion often leads to mental bravado or recklessness, as the ego needs to prove itself. This mental insecurity can also manifest in your having such a need to prove yourself mentally that you are overly aggressive and argumentative. 

Mercury in the 11th House:

Mercury is well placed in the 11th House, which is ruled by Uranus.  Uranus is said to be Mercury's higher octave - Mercury being associated with the mundane mind and Uranus being associated with the higher mind. Thus, having Mercury in the 11th House tends to elevate Mercury's vibration. In the 11th House, the mind is drawn to consider things that lie beyond the ego, e.g., the individual's role and purpose in society. 

For the individual with Mercury in the 11th House, this often results in a tendency for you to identify with a group. It may be common for you to take on the role of communicator and information processor in a group situation. You are also mentally inclined toward taking on social responsibility. If you have an active intellectual life, you are likely to find mental stimulation in the study of society, the individual and collective relationships to more complex systems, as well as in exploring ways to benefit humanity. 

Having Mercury in the 11th House, you are also likely to be mentally activated in group discussions or in working for a group or organization. You are likely to be future-oriented and open to new ideas. However, new ideas must be practical to be well received by you and you are likely to see abstraction for its own sake as useless. You tend to value your intellectual freedom highly.