The Sulphurites suffered a fourth consecutive League Two defeat - their eighth in 10 matches - when they went down 3-0 at Northampton on Easter Monday.
Results elsewhere mean that they are safe from relegation despite their wretched run of recent form, though Town's manager says his players need to stop shooting themselves in the foot if they are to improve on their current league position of 20th.
Simon Power's careless pass deep inside his own half set up the attack which led to Sam Hoskins eventually firing Northampton ahead 28 minutes into Monday's clash, before Leon Legge's under-cooked header back to Joe Cracknell and some particularly unconvincing goalkeeping by the latter gifted Louis Appere the Cobblers' second of the afternoon.
Hoskins then finished off a clinical break to put the promotion-chasing hosts three ahead, though the damage had already been done by that stage.
"The frustration from my point of view is that we are well in the game," said Weaver, who has been left to lament the cost of individual errors on numerous occasions this term.
"We are really in contention in games but the opposition just have to wait for the big mess-up moment which we are providing, and providing opportunities to score. These are the massive lessons of this season.
"I thought we passed the ball well at times and looked a decent outfit between both boxes. We knocked it about and I think the neutral would say that we had a game-plan and we knew what we were trying to achieve with it. We carved out opportunities, but at both ends we didn't do ourselves justice. We have to get better.
"If everybody had a little bit of Josh Austerfield's composure we probably score two or three today. And if we don't have the glaring mistake in us then we certainly don't concede at least two of those three goals. I don't think they [Northampton] have had to be outstanding by any stretch, but we have to learn to concede fewer mistakes .
"We've said to the players, play the brand of football that we practice in training, don't fear a misplaced pass. Thommo [George Thomson] was distraught because he gave the ball away and Northampton scored their third. He gave the ball away 70 yards from goal and we needed a rearguard action, to be able to react to that, but we haven't done that enough and it's something we have to progress in the summer."
Town travelled to Sixfields missing nine first-team players through injury and things got even worse for them after just 20 minutes of play when centre-half Will Smith went to ground clutching his leg.
"Will Smith has a twisted knee," Weaver added.
"We don't know the extent of the damage yet, but it's another defender out and it will amaze me if he's back before the end of the season."
Monday's result saw Harrogate slip two places in the League Two standings to 20th where they remain 10 points ahead of second-from-bottom Oldham Athletic - who lost 2-0 at Forest Green Rovers - with only three games remaining.
"The positive from today is that we get another shot at it next year," Weaver continued.
"It's not a Wycombe story or Sheffield United story where they go up twice in quick succession and then go back down."