Arsenal fell to a demoralising 3-1 defeat at Anfield that leaves them fifth in the Premier League having lost four of their last six matches across all competitions.
The Gunners were two goals down at half-time thanks to efforts from Roberto Firmino and Sadio Mane, and although Danny Welbeck pulled one back after the restart their defeat was confirmed when Georginio Wijnaldum sealed victory late on.
Bellerin - who played the full 90 minutes - felt the motivation within Arsenal's team was short of what is required.
"In the first half it didn't feel like we were ready and then we went 2-0 down," Bellerin told the club's website.
"We are very frustrated with how the game went. After the tough weeks we have had, the team should have gone onto the pitch, motivated and ready from the start.
"We need to realise that it is just not the way to go. We need to push harder, to start the games with a better attitude and just go for it because we showed that when we go for it and want something, we can do it."
The 21-year-old added: "It doesn't matter about the other team, when we have the ball and push hard, we can score goals. It is up to us to start the games with that desire, that motivation, and then we can get good results.
"We got one goal back and had a chance to make it 2-2, but sometimes it is too late. We just need to start the games better."