Many times in life we focus on our weakness, what we can't do or can't do well, rather than our strengths and what we can do and can do well.

You may also not be in a work or home environment which focuses on and emphasises your strengths, so you notice the external messages  emphasising what you perceive are  negative things about you, or believe others see weaknesses in you. If your mood is low or you are anxious you are even more likely to focus on these messages.

The awareness of your strengths is an something which is focused on by a branch of Psychology called Positive Psychology; it emphasises just this. The idea is that by being aware of your strengths, you can develop and strengthen what is right, enabling you to develop successful performance, character strength and resilience.