Brochas Lamed Beis amud aleph

In the academy of R. Yannai. ...Because of the silver and gold that You lavished on Israel... that is what caused them to make the golden calf. A parable, a lion does not roar in the midst of a basket of straw, but rather a basket of meat. R. Oshaya said: a parable of a person who had a cow that was lean and bony. He fed it vetch and it would kick him. R. Chiya bar Abba said in the name of R. Yochanan, this is analagous to a person who had a son. He bathed and anointed him, fed him and gave drink. He hung a purse around his neck and set him down outside a brothel. Do you expect him not to sin?

Why is there a need for three seperate parables. 

The Ben Yehoyada explains as follows: the lion is acting according to his innate nature and as such this is akin to a transgression committed "b'shogeg" (inadvertently). The cow in kicking out when fed is acting against its nature, which is a transgression committed "b'maized" (intentionally). Lastly the son who is left with money outside the brothel is akin to a transgression committed "shogeg hakoruv "l'maized" (a transgression which while nominally inadvertent could be expected to happen).

Klal Yisrael therefore claims that they should not be judged harshly for the Chet haEgel (the sin of the Golden Calf).  It is possible that it was contrary to our nature and we should have been able to withstand the Yeitzer Hara; but maybe it was rather that our sin was a function of an innate tayva (attraction) for Avodah Zara (idol worship); however, perhaps the most likely scenario is that the riches with which we were showered were too generous.

The comparison here is to Lot, on the second night post the destruction of Sdom. On the first night he became drunk and slept with his oldest daughter. When he became drunk the second night, he could not plead complete innocence. He should have been more aware.  So too, Hashem should have realised based on past experience that Klal Yisrael could not withstand the pressure to sin!