Fear can hold us back in many ways. When we are fearful it can stop us from pursuing any of our goals. Fear also tends to take away security. When you are insecure you feel like your not in a stable place and there's a possibility that you'll feel like you are just not capable of reaching your goals. Insecurity caused by fear can also make you unmotivated to even try. It can also make you feel like you are just not good enough or that you could easily fail and not make it to your goal.
(That was just a small answer. obviously more could be added to it if necessary)
Have a good day :)