"They were just rolling us and we weren't urgent enough to stop their kicks.
"They got four tries from kicks and that's just a soft effort by us.
"We're mentally weak there. It's just disgraceful and it hurts."
Arthur admitted his team had a problem of mentally staying in the game and lacked leadership when momentum would swing towards the opposition.
"When you play for 70 minutes, you're not going to win," he said.
"You have to learn to play for 80 minutes. The 80 minutes doesn't have to be all quality, but you've got to stay in the game mentally.
"We have players that just removed themselves out of that game for 10 minutes."
Skipper Tim Mannah will be assessed early in the week after being knocked out in an attempted tackle on Matt Scott before being taken from the field in a medicab late in the second half.
"He's got a pretty bad head knock, so we'll just have to wait and see," Arthur said.
The Eels, in equal last place with Manly, will next head to Melbourne to take on a State of Origin-depleted Storm on Monday.
"So it doesn't get any tougher going down there," Norman said.
"They don't have their Origin players there, but they've still got quality players. No matter who they put, they always show up and they always play for 80 minutes."
AAP me/jb
-AAP