Harrison has belief that Saints can slay the giants
While Saints can just about afford days like the one they endured at Bath in the Premiership, the Champions Cup is a whole different kettle of fish.
The teams are better, the players are bigger and stronger.
And the margin for error is minimal in each and every match.
That means pressure will be placed on the shoulders of the Saints players from the very start.
And they know that only a win will do when Lyon come calling at Franklin's Gardens on Sunday afternoon.
Lose, and you are immediately on the back foot, needing to probably prevail in at least two away matches as well as your next two home encounters.
So victory is vital this weekend.
But that is, of course, far easier said than done.
Especially as Lyon have only lost once in the Top 14 this season.
The French giants boast a formidable record, having won eight of their nine league games so far.
The defeat came at a ground Saints know well, with Clermont Auvergne managing to edge out the current table-toppers at Stade Marcel Michelin.
And somehow Saints must emulate their old foes if they are to secure the start they desperately need in Pool 1, which also contains Leinster and Benetton.
"It was a big focus for us last year to get back into the big boys' league and we're there now so we're excited to get out there and do the club proud," said Saints co-captain Teimana Harrison.
"If you can win all your home games and either pick up a win or losing bonus point on the road, it stands you in good stead.
"But the home games are must wins for us."
So can Saints really hope to compete with a team packed full of giants and flair, especially when you consider they lost all three Challenge Cup games against Clermont last season?
"You look back at last year and we did put Clermont under pressure a few times," said Harrison, who scored a hat-trick at Stade Marcel Michelin in a pool game back in January.
"These clubs have got big guys and good resources, but so do we.
"We can put teams to the sword, we've just got to get our drill right and we'll be good."
Saints didn't get their drill right last weekend as they were beaten 22-13 at Bath.
It was a horribly frustrating day for Chris Boyd's side, who had won all three of their Gallagher Premiership games ahead of the trip to The Rec.
"That defeat was the difference between a really, really good start to the season and a good start to the season," Harrison said.
"It does hurt because we'd love to go into the Champions Cup four from four."