Reish Lakish teaches us in the name of Reb Elazar ben Azarya that one should never differentiate between his children; that is to say to treat one child more favorably than the other. For as we see Yaakov Avinu's gifting Yosef the Kesones Pasim resulted in his brothers hating him, selling him down to Mitzrayim, to be followed by Yaakov and the shevatim themselves and ultimately resulting in all of Klal Yisroel being enslaved in Galus Mitzrayim.
Astounding! Didn't Yaakov Avinu understand this himself? He surely didn't need Reish Lakish's practical parental advice to anticipate the consequences of favoring one son over another - even if not to the ultimate outcome of galus Mitzrayim, but at least to not promote envy and animosity between his children!
Additionally didn't Yaakov know the Midrash (Tanchuma 4 see Rashi) explaining the name of the coat "Pasim" was an acronym for the future troubles it would be the direct result of for Yosef (Potiphar, Socharim, Yishmaeilim & Midyanim)? Why then would he "lovingly" gift it to Yosef - knowing that it would cause envy, hatred and 22 years of troubles for his beloved son?!
Finally the Gemara Shabbos expounding on the historical establishment of Chanukah explains that the year after the miracles of Chanukah the Rabbis establish the holiday, "l'hallel u'l'hodah" for "praise and thanksgiving". One wonders a) why they waited till the next year before establishing the Yom Tov of Chanukah and b) what difference is there between "praise" and "thanksgiving", aren't they synonymous?