The Magpies had eight more inside 50s than the Saints, but registered six fewer goals on the way to a 28-point loss at Etihad Stadium.
"We just kicked ourselves out of it. If you can't kick goals, you can't win," Swan said.
"Unfortunately we just couldn't put scoreboard pressure on them.
"It flattens you a bit, but you have to give credit to the Saints. They hung in there when we were getting it inside 50 a lot - we just couldn't capitalise.
"It eventually turned for them and they blew us away in the last quarter."
But while shots on goal were sailing wide - the Magpies kicked nine behinds without a goal in the second half - Swan felt the delivery into the attacking arc was equally to blame for the disappointing outcome.
"We probably kicked in long a bit too much," he said.
"Sam Gilbert took 20 marks and that's just something we'll have to address on Monday when we look at the tape.
"We'll have to lower our eyes a bit and look for a target instead of bombing away because we know Gilbert would try and get loose and sit back there. We played right into their hands and he killed us."
Swan denied the sight of St Kilda danger man Nick Riewoldt hobbling off just before half time had lulled some of his teammates into thinking the game was almost in their keeping.
"He wasn't the difference in the game before half time anyway," he said.
"I thought we kept him in reasonable check considering how much of a superstar he is.
"It just demoralises you when you go and kick point after point after point.
"Psychologically that hurts and that was the tale of the tape."
