Board Thread:Warhammer 40k General Discussion/@comment-24944355-20140706083220/@comment-24944355-20140707094204

Not immune but he was aware of his own flaws and was ever on guard against them unlike Horus, nor did he have Horus ambition. Also unlike Horus Sanguinious didn't feel abandoned when the Emperor left for earth nor was insulted by the creation of the administrum, he was much more accepting of the Emperor's choices & felt that the Emperor would tell his sons what he was up to when he was ready.

The only weakness that chaos could try to exploit was the red thirst, the flaw that Sanguinious was desperately trying to cure. Chaos would have tried to tempt Sanguinious with a false cure like they did with Magnus. Sanguinious though lacked Magnus blind arrogance and would have been far more suspicious & less likely to fall into that trap.