A wizard is a wise man, not just some spellslinger. A wizard is expected to understand matters,
You mean, like understanding that when a woman takes off her clothes for you, she's hitting on you? Because as I recall, Harry didn't understand that one until it was pointed out to him.
To understand oneself and to understand others and ultimately to understand the universe. That is what wizards are. Casting spells is the least of a wizard's role. Wisdom and intelligence is the main portion.
I know that Harry goes on about this in Storm Front, but Jim has gone on record saying that he wrote Harry as the magical equivalent of a plumber, so I chalk it up to early installment weirdness.
Making a mistake is not a sin , but not learning from those mistake defenitely is a sin. That is what the gatekeeper say in book 4.
When did Harry not learn from his mistake? He hasn't let Murphy
or any of his other allies hit him
after Fool Moon--when she tried it (albeit under the influence of mind control) he defended himself and knocked her out.
If 6 years has gone by and Harry still can't recognize that Murphy is manipulating him, well, what is Harry been learning all this time?
I'll repeat myself.
Murphy is not manipulating Harry for most of the books. She manipulated him in one to three of them. She definitely manipulated him in Storm Front--even Harry acknowledged that. She didn't manipulate him in Fool Moon--she assaulted him, which is a different thing. She didn't manipulate him in Grave Peril, Summer Knight, Death Masks, Blood Rites, Dead Beat, Proven Guilty, White Night, Small Favor, Turn Coat, Changes, or Ghost Story. I view her as manipulating Harry in Cold Days, but I have acknowledged that that is not what Jim intended. As a direct result of my interpretation of her behavior in Cold Days, I also believe that she manipulated Harry in Skin Game.
Not to mention that he is still get manipulated in book 14 in some people's opinion.
There's a quote from Murphy in Turn Coat that is appropriate here.
"The reason treachery is so reveiled," she [Murphy] said in a careful tone of voice, "is because it usually comes from someone you didn't think could possibly do such a thing.”
Harry is in a position to get manipulated by Murphy because it would
never occur to him that she would do so. She's spent the last 11 books demonstrating that he could trust her.