United needed two stoppage-time goals from substitute Scott McTominay to avoid a third successive defeat at Old Trafford.
Afterward, Ten Hag said his team had been “eaten” by Brentford in the first half and urged his players to be more “determined.”
“When you can’t handle the pressure, don’t play here,” Ten Hag said.
“Those players, they are so experienced. These are such high-quality players so they have to take responsibility.
“In football it is eat or get eaten. Too many times in the first half of this season we got eaten by opponents who are more hungry. This can’t be. It has to go away. Every player has to deliver that in every second he is on the pitch.
“That is the demand, the standard, when you do that we have seen last season you get a determined team. We were not always determined on every occasion in games, and you get hammered for it. This has to change.”
They resume in two weeks with a trip to Sheffield United and Ten Hag has urged his team to use McTominay’s late goals as a trigger to turnaround what has been a disappointing start to the season.
“We didn’t allow them one shot and we had some opportunities and then the same story again, we conceded a goal on a decisive moment, totally the wrong decision,” Ten Hag said.
“We started and we were not in formation, an easy giveaway and it sums up our season. Such easy giveaways, you get punished in top football. We have too good players to act like this. It has to be a turning point but also a restart because we have to get into higher levels.
“The spirit is good, the belief is good and the team is together. We have shown that, we have shown strong character. It can be a turning point but it is up to us.”
Meanwhile, Brentford boss Thomas Frank described the defeat as “brutal” after his team came within minutes of a first win at Old Trafford since 1937.
“I think we did so many things right, coming here to Old Trafford, almost perfect first half, pressed high, good on the counter and a well deserved lead,” he said.
“Football is brutal in moments like this. At least a draw was probably a fairer reflection.”