What causes Pip to regret his thanklessness toward Joe in Chapter 52 of Great Expectations by Charles Dickens?

There are many points in the novel in which Pip reflects
on his bad behavior toward Joe.  In Chapter 52, the injured Pip, who is unable to cut
his own dinner, has a conversation with the landlord at the inn while the landlord cuts
his food for him. It is this conversation that causes Pip to feel worse about his
behavior than ever before.

The landlord, not recognizing
Pip as the same child he used to know (and thus not knowing to whom he was speaking),
proceeds to explain that Mr. Pumblechook "done everything" for Pip, and that Pip "gives
the cold shoulder to the man that made him" each time he returns to the
village. 

As Pumblechook always took credit for being Pip's
first benefactor, Pip is angered by this conversation.  Further, he thinks about all Joe
has done for him, and acknowledges that Joe has never taken any
credit for anything he's done for Pip:

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I have never been struck at so keenly for my
thanklessness to Joe, as through the brazen impostor Pumblechook.  The falser he, the
truer Joe; the meaner he, the nobler
Joe.