I imagine that Jacob is referring to some aspect of himself.
It could either be his 'past self' - i.e. Jacob before he learned to be a stylish womanizer, perhaps - or it could be the nice and sentimental part of him that still exists in his character.
(We know that some part of him like that exists because he falls in love with Cal's daughter.)
I imagine it is some combination of the two.
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Nobody realises this, but Jacob fell in love with Hannah instantly and helps Cal because he reminds Jacob of Hannah.
Jacob never thinks "you remind me of Hannah," but he just feels some sort of connection to him.
Hannah doesn't display any qualities of Cal but it's some sort of psychic thing.
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If I remember right, Jacob once said that his dad was kind of too honest, too fair or something.
That is why his wife (Jacob's mom) treated him not in a good way (maybe cheated
too)Maybe it was the scene where Hannah and him are chatting in his bedroom.
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This is something I too pondered, however thanks to DVR and rewind/replay you can see that Gossling's character Jacob actually answers Carrell's character Cal's question "Why are you doing this?"
with "Maybe you remind me of ME" - the Audio track was edited in post production to what we all hear, "Maybe you remind me of SOMEONE".
Because Gossling's facial expression and limited mouth movement when he speaks... it was an easy edit to make and unless your looking for it will probably easily miss.
As for my theory for the change...
I understand a fair amount of Gossling's lines were ad libbed.
To that end, When he's in bed with Stone's character Emma and they're talking and Jacob asks for 'a kindness' and reveals his fathers softness and that his mother easily took advantage of him is part one element.
My additional association is that when Hanna blows him off in the bar and he gives her the long stare... I think he also see's Hanna in Cal.
My reason for the latter is Jacob says the same line when he 'honks' both of their noses.
I realize Jacob's character is shocked when he ultimately meets Cal in the back yard 'meet the Mother & daughters - however, I still think there is some subliminal and intriguing tie between what he sees in Father Weaver and Daughter Weaver characters.
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I too also pondered this, I even found this website looking for the answer.
However, I think I've solved it.
Jacob describes his parents at one point in the evening with Hannah, he says his mother was cold and vain and his father couldn't handle her.
It makes for a strong argument that Jacob's parents got a divorce, and his father either died shortly after from that broken heart syndrome, or committed suicide.
Realistically Jacob in this movie can't be older then early thirties.
So for him to have had all this wealth and time to "try and buy happiness
" his father must have died some time ago.
id say at least a few years, if not more.
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It's not Hannah, it's Jacob's father.
He describes Cal when he is in the bedroom with Hannah.
He calls him for fatherly advice when he is about to meet Hannah's mother.
Cal gives off a fatherly vibe.
From the moment that Jacob meets him he's devastated about his family falling apart, showing Jacob how important family is to him.
Jacob was looking for a father figure and he saw it in Cal and wanted to help him and have him play a key role in his life.
That's why it's so difficult for Jacob to have Cal angry with him and Hannah, it's why he craves his approval and why he's so hurt when Cal doesn't give it to him.
I don't think that Jacob was ever any different than he is in the movie-
I think he was always a womanizer.
Even if the line was originally "Maybe you remind me of me" then they would have changed it to suit the purpose of Cal being a father figure.
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Cal reminds Jacob of his father.
The qualities of being kind and sweet he describes to Hanna in the bedroom are traits that I believe Cal has.
Proof of this is when the kids stay up and Jessica talks to Emily.
Jessica told Emily "That when she babysits most kids will stay up late for moms but not for dad."
He also said his father was very successful in business.
Cal works for a business firm in the movie.
Jacob stated that his mother was very vain and that his father "couldn't handle her.
" Cal's progression in the movie though Jacob's help is evident.
Cal is devastated by Emily in the beginning of the movie.
Cal throughout the moviel is more vocal with Emily expressing how he feels about the situation.
This adds to what Jacob says to him when coming out of the fitting room, "Your wife cheated on you because you lost sight as who you are as husband, a father, and even a lover."
Cal admits towards the end of the movie he did not fight for his relationship.
Jacob lost his father very young according to the movie.
Perhaps he helps Cal because he sees him headed down the same potential path as his father.
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It is meant to mean Cal reminds him of himself.
It's not that hard, this line makes you immediately think that Jacob is talking about himself, not his father.
He didn't even mention his father until later.
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In the bar Cal and Jacob meet for the first time in  Crazy, Stupid, Love .  Cal asks Jacob why he is helping him (Cal), to which Jacob replies   Maybe you remind me of someone   Who is Jacob referring to? Is it his father?
Who did Cal Weaver remind Jacob of in Crazy Stupid Love?
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Jacob helps Cal because he reminds him of Hannah, who he instantly fell in love with.  Jacob fell in love with Hannah instantly
Nobody realises this, but Jacob fell in love with Hannah instantly. Hannah doesn't display any qualities of Cal but it's some sort of psychic thing.