I disagree, for me a lot of my characters have an aspect of myself that I explore from their eyes thus I become one with my characters and my characters become one with me.
Its how I give my characters humanity.
Also, one can have contradictory characteristics without it being bad writing for example I have a character who has one hell of a temper and can tear your arms off in a second... yet she is also very compassionate and while yes she has a bit of a rough edge to her, she can be very kind and sympathetic.
You see there is this thing called a three-dimensional character unless for some reason characters with only one personality trait are the only good characters out there while most out there hate flat characters.
I think I didn't word it right.
I tend to type a few words at a time since I consider it a bother to think and type for long.
For the first part, I meant that having your own present thoughts spill from the character ruins it. For example, the character is the serious type, yet the author can't resist to make a joke and made the serious type make a funny joke which is out of his personality. Clarifying further, the serious character is fitting to make sardonic or cynical jokes but since the author don't do dark humor, he made the character say light-hearted humour which is out of character. Exception is if it's related to plot
For second part, say we got boy A. He really loves girl A but he gave his love to girl B. If all this happen not of his character or for no reason, this is bad writing. Now I said unless, if the exception is if girl B tempted him and he fell for it. Despite him really loving girl A, he fell for girl B because he got tempted, this is the hypocritical part I'm talking about. This 'hypocrisy' makes him more of a human character.
(Srry for telling a story instead of explaining. I really can't put the second part into simple words)