User blog comment:B214/Volume 23 discussion blog/@comment-27083298-20170318234409/@comment-10330822-20170319040008

Actually, he has every right to be intimated by Crom. Besides, the core of Trihexa, Crom is the strongest thing Issei has fought, aside from maybe his scuffle with Sirzechs, of course, we don't know how strong Sirzechs is compared to Crom.

Remember, Rizevim was the strongest person Issei had defeated as of Volume 20, and in Volume 21 he defeated Apophis, who was even stronger. However, Crom Cruach is stronger than both of these people, hell, he's stronger that Ddraig himself. Ddraig also didn't even hold anything back when Issei asked, saying that Pseudo DxD would do nothing, proving Issei is out-classed if he doesn't use at least DxD G.

Also, that is what I am saying, Issei is literally fighting stronger and stronger people constantly, true, he always rises to the occassion, but it has to be disheartening to know that every single time you reach a new level of power, there's always someone above you to make you feel weak.

Of course, its not like it affects Issei, because Issei always views himself as weak. That is what the anon was talking about.