The West Yorkshire club have made great strides since he took over with them bottom of Super League in May, including a memorable win at Wigan.
They almost produced something similar after fighting back from 36-4 down at Huddersfield Giants yesterday to get within eight points of the new front-runners.
Castleford eventually fell short losing 48-32 and it left Powell admittedly scratching his head once more.
“It was really disappointing, the first half,” he said. “I think we had half the sets they had – we had 11 and they had 20-odd.
“We completed 40 per cent of those and you can’t do anything with figures like that.
“But I thought we sorted a few attitude things out at half-time and then we started to play.
“We know we can do that. The problem is we’ve got to change the mentality in the team.
“We had a pretty frank chat about that after the game.
“We just gave ourselves too much to do. It’s a tough game when you give that much away in a half of football.”
Castleford – who remain in 12th spot – continually score points for fun but annoyingly switch off for long periods. They changed that around in the second period but ultimately it was too late.
“The effort from everybody was magnificent and I thought we were by far the better side in the second half,” added Powell.
“But there are some key lessons to be learned in terms of our attitude and approach to games.
“We have got to sort that out or we’re not going to win consistently. We are not learning quick enough.
“I think we’ve got to believe we can win games like that – I don’t see any reason why not.
“I am trying to sell that belief to the players. We conceded way too many points, but we scored enough to win a game, again.”
Castleford’s second-half endeavours were all the more remarkable given they had been without injured props Jonathan Walker (knee) and Ben Davies (back) since the 10th minute.
Fellow forward Oliver Holmes (knee) joined them on the bench in the final quarter leaving Powell with barely any interchange options and perhaps wishing he had included Keith Mason, the front-row who spent much of last week in court successfully winning his case for unfair dismissal against Huddersfield.