O'Neil described the 5-3 result at the time as the worst of his career.
Wolves meet Manchester City on Sunday and the Wolves manager said: “The Brentford game was a real shock, and maybe a shot in the arms for everybody. If we're not at it and we're going to make mistakes, it's not just the top teams that are going to beat us in this league. If you turn up and you just make unbelievable mistakes for goals, everybody in this league is going to beat you. So that can't happen.
"Maybe off the back of a bad run you see Brentford come in at the end of it and you think, ‘OK, let's go to Brentford and let's win’. It's never, ever going to be that easy. You need to take care of all the bits around your game.
“We conceded some goals that were almost unexplainable, and it did then just snowball into an afternoon where the game never really got going for us. We were always chasing, and you end up opening up and causing some problems to yourself. So, a bad day for us, the Brentford day, but one that hopefully lets the lads realise that no matter who we play at this level, we need to be 100 per cent on our game.”
He also said on Friday: “Points wise, it’s obviously bad. Very bad. I'll be the biggest critic of my team, I know we will face criticism from outside, but I'll have the most critical opinion and I felt a real need to be critical of them after the second half against Chelsea, the second half against Aston Villa and the 90 minutes at Brentford. I thought we were below our own standards in those, but the rest of it we've given a good go against some tough opposition, and come up a bit short."