"Growth Mindset" is a conscious or subconscious belief that:
"Whatever I want to become better at, I need to invest more time doing it. The more experience I acquire, the more I will grow, and the more skilled I will become."
We all have insecurities about ourselves in certain areas such as public speaking, relationships, negotiation, money, competition, math, or creativity. Our insecurities are normal and are not the real issue. The real issue is many of us feel powerless to conquer our fears for a better life. Instead of thinking with a "Growth Mindset", many of us developed a "Fixed Mindset" as we grow into adulthood.
People with a "Fixed Mindset" subconsciously believe that how far their abilities can develop in their lifetime have been determined at birth-time.
This false belief greatly limits what our minds would consider as possible. When a person with a fixed mindset attempts at something and it didn't work out well on the first few tries, one may conclude that he or she is not talented enough to perform well on it ever. Sooner or later they will conclude that they are good at nothing because there are few things that we can excel just after a few attempts.
The following diagram compares "Fixed Mindset" and "Growth Mindset".
People with fixed mindsets may overestimate their talent and ability in certain areas and are eager to prove themselves. But as they encounter failures, they draw premature conclusions that they are wrong and feel beaten up. The stay in areas they can do well in which become their comfort zone. They feel insecure to take on challenges outside of the comfort zone and believe they are doomed for life in all other areas.
People with growth mindsets, however, will not presume what they are good at or not. They follow their interests and goals. If there is an area that they think they need to improve to reach their goals, they invest time in it to gain more experience. Because they know becoming sufficiently good at a skill only requires learning and practice, not extraordinary in-born talents.
You can learn more about "Growth Mindset" in the book "Mindset" by Dr. Carol Dweck, a renowned professor of Psychology at Stanford University who first pinpointed the concept.