The Blues' unbeaten run in League One came to a disappointing close as they fell to a 2-0 defeat to struggling Gillingham at Fratton Park on Saturday.
The Gills had gone 10 games without a win '“Â a run stretching back to August 11 '“ but punished Jackett's men twice in the first half, before withstanding the home side's second-half onslaught.
It meant hope of bettering the club's record 13-game league run without defeat wasÂ dashed in front of a crowd of 18,158.
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But it was the inability to make the most of their possession which angered Jackett as he pinpointed a shortfall in aggression and hunger to get on the end of deliveriesÂ from his side.
He said: '˜The shots weren't coming and that was frustrating for myself.
'˜They were solid defensively, but we didn't do enough on the ball and get the shots in which the possession in both halves warranted.
'˜It's something we have to make sure we do better in.
'˜We got into good situations. We had a lot of set-pieces.
'˜In the second-half we had enough time and enough pressure to get back into it.
'˜The two centre-halve headed, blocked and kicked everything. They gave us very few openings.
'˜But I felt the service was good into their box from the corners '“Â and I didn't see us having enough desire to get on the end of it, basically.
'˜You do need that. With the way the crowd are here, one goal turns the game.
'˜We got down our left-hand side a number of times and either checked out, hit the shot over the bar or put crosses in the box and didn't have the desire to get on the end of the ball.
'˜We didn't find that aggression or touch in the box to make a difference, and, fair play, Gillingham did. That's why they won.'
The loss means Pompey have been held twice and defeated by sides in the lower reaches of the table on their past three home outings.
Jackett took solace from the fact Pompey remain three points clear at the head of League One after both Peterborough and Doncaster suffered heavy defeats.
His side have accumulated 27 points from 12 games '“ which still sits at an impressive 2.25 points per game.
Jackett added: '˜Points total is a big thing. That's what I look at for the stage of the season.
'˜Our points total is high and that's a good thing.
'˜But I'm frustrated because we had the lion's share of possession and we didn't work their keeper enough. That's a frustration for me.'