It is a cliché that has seemingly been around ever since football was invented.
But the proverbial game of two halves was certainly evidenced when Gillingham arrived at Fratton Park.
Pompey dominated the first half and forged ahead through Jamal Lowe, only to spurn several chances to extend that lead against opponents who looked in disarray.
It was a different story after the break, though, with the Gills now displaying plenty of confidence and scoring some impressive goals.
Lee Martin’s brace added to Conor Wilkinson’s leveller and left Kenny Jackett bemoaning his side’s defensive frailties.
The Blues boss said: “It was a good first half from us and we could well have been further ahead.
“There was a lot of promise and it was nice goal from Jamal, while there were other opportunities for us.
"In too many games of late we’re looking brittle in defensive situations and there are moments when a lack of talking and experience is costing us."
“He went through again, while Connor Ronan hit the post after the break and there was also a chance for Dion Donohue.
“Gillingham started the second half very well and I understand the strikes they had were particularly impressive.
“But we need to cope with periods of pressure without conceding. It’s something we’re not doing and it’s costing us.
“We can talk about the quality of their strikes, but it’s just too many goals that we’re conceding of late. They were avoidable and it gave us a mountain to climb at the end.
“In too many games of late we’re looking brittle in defensive situations and there are moments when a lack of talking and experience is costing us.
“We just have to keep working with this group because there’s potential there. We’ll work on what we can do better and focus on trying to have a strong end to the season.”
There was one piece of good news for Pompey, with a fit-again Jack Whatmough making his first appearance since the start of September.
Jackett said: “Jack’s been unlucky with injuries in his short career, but I rate him as a player and he showed a lot of promise.
“But Oli Hawkins got a hamstring strain in training on Friday. It’s a grade one, which isn’t a high level, but I would think he’ll be out for a few weeks.”