User blog comment:B214/Chapter 498: Gray vs. Invel/@comment-5303512-20160822105845/@comment-5303512-20160822113714

Well, it would be more complicated than that, Gray could have the same reaction as Natsu when he learned that he is E.N.D. so he would most likely deny it or even forgive him, so Invel needs to push him over the edge.

Or in the Joker's own words "Madnass as you know is like Gravity, all it takes is a little push." And no one argues with the Joker! LOL