Insecurity can destroy your confidence more probably because it will show in the way that you carry yourself. There are some people who may not actually be confident in the beginning, but they try to figure out what is causing them to become insecure. Once they know the cause, that is the time when they can start working on their insecurities.
Most people will feel insecure from time to time, but there are also some people who feel insecure all the time. These are people who may need help or may need a stronger support group to make them feel that they can transform their insecurity into something that will be good for them.
Insecurity can most definitely have an effect on confidence but I think it depends on how much you dwell on the insecurity. It’s perfectly normal to feel insecure from time to time but if you focus on it too much, you will negatively impact your confidence. One way to not dwell on insecurity is to write down the things you feel insecure about and then objectively analyze them, one at a time, if necessary.
Insecurity has a lot to do with uncertainty and if you can come up with solutions to remove or lessen the impacts of the uncertainties, you can take actions to feel better and improve your confidence.