Hassell said: "That was definitely two points dropped. Being 1-0 up at 85 minutes you have to close a game out and that's been our Achilles heel for the last five or six games.
"We're not learning from our mistakes. We're dropping deep as a team and, inevitably, teams keep getting one chance and keep sticking it in the back of the net against us.
"We now have a massive game and we need to go to Plymouth and pick up three points. We have approached games really well and have been 1-0 up in the last four of five games, but then panic sets in because you know you're five minutes from safety."
Hassell added: "We've dropped 10 points in our last seven games, so if we go down we only have ourselves to blame, definitely."