‘No More Mr. Nice Guy’ talks about The Integrated Male and one of the qualities being ‘he has a strong sense of self.’ What does that mean?

‘No More Mr. Nice Guy’ lists a few attributes that an Integrated Male has and the first one is:

‘He has a strong sense of self. He likes himself just the way he is.’

What does the ‘strong sense of self’ mean? Does it mean knowing who you are? It’s my understanding that the ‘he likes himself just the way he is’ is loving one’s self, but I’m confused as to the meaning as a ‘strong sense of self.’