The Opposition between the Sun and Mars is a dynamic aspect, producing a great deal of energy that can occasionally be difficult to handle. At times you may over-react to what you think to be challenges from others, forcefully asserting your opinions. Compromise is not your strongest point.
You probably do not see yourself as particularly aggressive, you simply react according to what you expect to get from others. Something has made you feel defensive about yourself and the best form of defence is to attack first. The most likely arena for this behaviour is in your close personal relationships, or perhaps you will form a relationship with someone else who behaves in this way, which is often the case with Opposition aspects.
When you realise that everyone is not out to challenge you, you can channel this energy in more productive directions. You have a tireless drive to achieve whatever it is you want for yourself. You can be a champion for some cause and fight selflessly for the rights of others.