The Cottagers lost 4-3 on the day at Elland Road to remain pointless after their opening two games.
Parker said, "There were a lot of encouraging things. You go 4-1 down away from home and they could really drop their heads. I didn't see that in my team. I saw a real character and determination.
"The biggest thought in my head is that you cannot give up goals that we have given up today. You can't expect to score four or five goals to win football matches in this league.
"If you give up goals too easy you aren't going to win many. I just worry that a red bolt doesn't go off for us. We need to smell it [danger] and sense it in those moments that are crucial in games. Sometimes we are a bit too nice.
"I see an innocence about them not being streetwise. Overall there are a lot of positives but there was one negative which I realise is going to be the difference between us getting results or not."