The views of others are always incomplete - they are not with us all the time.
However, the way in which we see ourselves can be very slanted. Being critically honest of oneself is rare. Denial is a very common condition!
On balance, I think I know myself better than anyone else knows me, partly because I've spent a fair amount of my life wondering about who I am and what I think. No one else has ever been as interested in me as I am!
To indicate what defining characteristics I have would be to put this in terms of comparison with others, which is something that others may do better than me...because they can compare Peter to Paul and Pamela, etc...all of whom are third parties to them.
...but why should I care if they think I'm "arrogant", for example? If I think I'm damn good, I'm not going to criticise myself for it!