Planets move in retrograde to reconsider and rethink or revisit the impact or change they left on our lives. We could think of it this way: what was done previously or any influence or changes in life recently observed need a revision or improvement. There could be some modifications, repetitions, corrections and / or change of mode necessary before making things permanent. So it is more like double checking!
Retrograde planets are usually about self reflecting a person's quality. For example, Jupiter retrograde people are agnostics or atheists and philosophers. But at the same time it kind of decreases the positive properties of that planet. Only exceptions are Mercury and Saturn.
Saturn retrograde is a blessing as this means now Saturn will open up the boundaries and limitations it has set up for you although it will make you work hard but you will almost always yield the fruits of your labor.
In case of Mars, the person will not be able to know where to expend or focus his energies or he may not allocate any energy or may not make any efforts at all!
Mercury retrograde makes the person very careful and anxious in communication and while doing anything related to mercury like logical reasoning, mathematical calculations or writing an email they'll think more than normal person does! Basically the type of people who will calculate 1.5+1.5 on calculator and see if the answer comes to 3 or not just to be sure. So in a way it strengthens the mercurian properties.
However, by just looking at one planet, you cannot completely define the personality. There are lots of other combinations, planetary placements (Rashi) and conjunctions that you have to take into consideration. Especially conjunction with a malefic/benefic and aspect of a malefic/benefic. Those alter the results of retrogression significantly.
