There are many ways you can tell the difference between a confident person (CP) and an over-confident person (OCP). Here are just a few. A CP will recognize their imperfections and work to improve themselves; an OCP thinks they’re perfect. A CP will offer to help others because they believe they have something of value to offer; an OCP expects others will fail without their help.
A CP will also accept help from others; an OCP doesn’t really want any help because they think they know it all. A CP knows failure is possible and will take responsibility for their actions; an OCP will never admit failure and will blame others if there is a failure.