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In General, our best qualities is something we develop, it takes time, experience, and applied knowledge to get it right.

Our worst qualities are what we neglect or are in denial about ourselves.

Here's an example for myself, one of my worst quality is my opinion, basically i seem to default to contradicting and generally too opinionated for my own good, but ironically, it can also be my best quality, if i temper it with timing, and thoughtfulness, a dash of empathy, and also do my homework first so when i share my opinion, it is in context and in consideration to the consensus even if it's an opposing opinion

my best quality is the good part of my character or attitude which people admire. While my worst quality is the bad part of my character or attitude which people dislike even though sometimes it but at most times I would like to change the attitude to something much more adorable.