This emotion when handled well can drive someone to learn, excel and even be more respected since overcoming this emotion can be seen as courageous by some. However, there can be a fine line between being insecure and becoming narcissistic and guarded. Taking an offensive stance/action against this emotion can be seen by others as something quite annoying. I've seen several people who like to show off with what they believe is something they excel in because they are insecure with themselves. This makes them seem dishonest, unimpressive and a braggart...sometimes they also look like a fool or a tool. Unhealthy insecurity is when someone tries to instigate/makes competition when there is actually none.
Insecurity when driven by ego can be disastrous and can lead to fractured friendships and severed relationships. Insecurity can also lead to other emotions such as envy and jealousy. But, there is a plus to this as with any other emotion, insecurity can drive someone to really study and to be better as a person. (example: if one is insecure with the lack of physical appearance, they work in developing a better personality.)
The best weapon against this emotion is to be happy with yourself and to accept your weaknesses, this way you can find the chips in your armor instead of blaming others for your issues. Never let it dictate the way you act or form your personality. This emotion can also keep you from the things you desire most. Don't let insecurities hurt you.
Everyone can have a trace of insecurity (I do), and it can be healthy as long as you don't put pride or ego before it...Hard to explain, I guess I need to do a full write up on this one.