User blog comment:B214/Shin DxD 1 discussion/@comment-36663391-20180920083134/@comment-2601:87:8300:20D0:71FA:4921:65C5:7FA9-20180922022215

The reason is his pride and I don't know about you, but even after reading that fight I'm still not convinced they both gave it there all. I  thinking maybe 80% and it's hard to imagine anything that Issei can surpass his limits but Vali cannot with his strength.