Andy Last stressed his side must improve after victory over Wakefield.
Hull triumphed over Trinity 26-23 to register a second win in four games under the interim head coach.
But, while Last was relieved to pick up the win, he was left disappointed with elements of his side’s performance.
“With the close nature of the contest it would have been devastating to lose it late on,” Last said.
“That would have given us a real kick in the guts leading into a game on Sunday against Castleford.
“I spoke to the boys before they gave a very rousing rendition of Old Faithful and just said I wasn’t happy with the first half, I felt we made too many unforced errors from key individuals because we don’t want to trust and believe in the process of what it takes to win a rugby league game.
“There’s elements when you’ve just got to get to the end of your set, kick, chase and defend. We’ve got to be better doing that.
“We didn’t do that well enough in the first half. I thought in the second half we did a better job of that and we showed that character and desire which is something we can build on moving forward.”