Neale Cooper says Hartlepool were undone by their chronic inability to "put the ball in the net" after a 2-1 home defeat to Chesterfield.
Pools were well on top in the first half and for the opening period of the second-half, but all they had to show was Gary Liddle's 37th-minute finish and, with visiting keeper Tommy Lee making a number of impressive saves, the vital second goal would not arrive.
Two second-half strikes from impressive substitute Danny Whitaker and fellow Chesterfield striker Jordan Bowery turned a one-goal deficit into a victory.
Cooper said: "If you don't take chances, you won't win games. We battered them first-half. But we were sloppy with it at times. Some of the passing was sloppy from the start, giving them the ball back.
"Chesterfield work hard and have goals in them, this was a major disappointment for us. Shape went a wee bit, full backs pushed on and were caught out. It's really disappointing.
"There was pressure on the boys and I need players who can handle that. We had chances and didn't take them, they took theirs. Defensively we've generally been very good, but we don't put the ball in the net."