The defending Premier League champions slipped to seventh on the table after Thursday's loss to Chelsea at Anfield.
Speaking to Sky Sports after the final whistle, Robertson said: "These games are won and lost on fine margins and these goals can't happen. For us to get beaten on the counter-attack is not good enough.
"Five home games without a win, that is nowhere near good enough. Nothing is going to help the fans at home and it is simply not good enough because games are running out for what we want.
"Too many heads are going down when we go 1-0 down, we can't do that. Football is about taking knocks.
"We can't rely on the past. Last season is over with, it is done. We have nowhere near been good enough to what a Liverpool team should be. We are dropping further and it is not good enough.
"Games are running out and we need to put the pressure on the teams below us. People will think we are down and out and we need to get the results to show them we are not. At the moment we are not doing that."