Kevin Nugent was disappointed with his side's first-half performance in Tuesday afternoon's 3-0 Professional Development League defeat to Cardiff City - but praised a "spirited" showing after the break.
George Alexander was shown a red card on the stroke of half-time in South Wales with the score at 2-0, with The Bluebirds adding a third late on in soaking wet conditions.
"I was very disappointed with the first-half especially, we looked disjointed," Nugent told millwallfc.co.uk. "We finished the game with seven scholars in the team. We conceded some poor and preventable goals in terms of our defensive shape.
"We then went down to 10 men and we had to shuffle the shape numerous times, but the second-half was a much more spirited performance.
"We kept a tight shape and had to keep ourselves in the game for as long as possible and then maybe go for it. We had plenty of corners and some shots, but it wasn't to be."
The Under 23s are now winless in five, and the manager explained his post-match thoughts to his players in their attempts to get back into form.
"Again, it's a learning curve for the players. We're on a bit of a difficult run at the moment and they've got to dig themselves out of it. We've got some young lads, so it's good experience for them, but we've also got some in and around the first-team, which is the important part of it.
"We've told them that being a footballer isn't just about having the ball at your feet - it's about your personality, your courage, your heart, numerous things. It's all about learning, so hopefully they can take lessons from today's game, as well as recent performances. We should've been picking up points and winning games recently, but we're ending up with draws and defeats."