The extremely obvious/blatant motive fueling 90% to 95% of those who call Blake "a pussy", or anything to that effect, can accurately be described as blatant cases of them "hating"/being envious.
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The other 5% to 10%, at absolute most, is simply a result of Blake not having any sort of "bodyguard"/"old school"/"protector" teammate(AKA: A Charles Oakley, David West, Bill Laimbeer type that watched his back while he was adjusting to the NBA and learning how to handle nightly cheap shots.
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On his team when he first came into the league -- AKA: a *Charles Oakley, David West, KG, 'Zo and Anthony Mason[RIP], etc. type --. As a result, Blake was subjected to a massive number of cheap shots game-in/game-out. All of this with no savy vet to watch his back, Blake got into the bad habit, which was bred out of legitimate necessity BTW, to use the refs as protection and to seek out calls.
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The above facts are a shame too as Blake has not once ever appeared to be(and or even temporarily acted like a "pussy" in any other respect either, or least in no other way that I have ever witnessed.
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One does not simply stroll into the NBA and not only leap over veteran players(figuratively and literally) who have put in more time and most of whom also possess massive egos without taking as many cheap shots and as much resistance that they can possibly get away with then adding in the fact that Blake had little to no "protection" from his frontcourt teammates during his first few seasons and here we are... ಠ⌣ಠ
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I will also add that since Barnes has joined the team and DeAndre has matured himself this is much less of a problem than it used to be and will likely disappear altogether in the near future.
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*-Charles Oakley was possibly the best at playing this role in the history of the NBA as he was certainly the best I have ever seen(last ~25 years or so).