You could sum up each of Munster's last three meetings with Toulouse in four words; nearly but not enough.
Three defeats, albeit one of those coming via a placekicking competition in an enthralling quarter-final last season. All three of those games decided by a single score.
Their European campaign was ended by the French giants in each of the last two seasons. And there's plenty on the line when they meet this Sunday at Stade Ernest Wallon.
With their fixture being the last of the weekend in Pool B, Munster have the advantage of knowing what they need to do. By the time they kick off in the south of France, Graham Rowntree's side will know what they need to advance to the last 16. It's possible their place in the next round will already be guaranteed by Saturday night.
But after three agonising defeats to Toulouse in just under two years, the latest being an 18-13 defeat at Thomond Park last December, says Ugo Mola's side have become their white whale.
"I don't think you can quantify it," he says, when asked how badly they want to end their run of defeats to the five-time champions.
"It's one of those where every time we were just one touch away from getting the win, one score games every time. We're getting so close.
"Based on what we've been doing this season, and our growth in the last six weeks especially, I think we're really positive and hopeful we can do something special this weekend."
And with Munster's confidence growing as the season progresses, Kleyn believes a win this weekend could potentially be season-changing.
"It would be incredible. Outside of what it would mean for us on the log, mentally it would be really big for us. We've been building confidence, and we've been building momentum, and I think if we were to get this win, the sky is the limit. Who can stop us, if we can beat Toulouse at home?" he added.
Kleyn's been a consistent presence in the Munster second row this season, with 13 starts, missing just three games in total.
His size and power was evident last weekend in their Round 3 win against Northampton Saints, latching on to Gavin Coombes twice in the first half to help drive the number 8 over for tries from close range.
And while those less glamorous jobs don't get much credit publicly, he says it doesn't go unseen by the coaches.
"I think between the four walls we notice those things, so I can't say I do it without any plaudits, but I don't mind doing the hard work.
"When you're latching someone like Gav, it's not all that hard work, he's a big, strong fella so he does a lot of it himself.
"But as long as the team wins at the end of the day and it's for the benefit of the team, I don't mind doing it."
Kleyn hasn't managed to score a try this season, but like many of his teammates, has looked more and more comfortable on the ball as the season has progressed, with Munster's players getting to grips with their new fast-paced gameplan.
"I think there's more of an onus on all players to use the skills they have. The way we're training at the moment, you're being exposed to those catch-pass situations, and it's just more cohesive.
"For me, I've been fortunate enough to stay injury free - touch wood - and that's really helped me. The more you play, the more consistently you play, the better you get. I think a lot of my form is due to the fact that I've been able to play a lot of rugby, which is brilliant."
"The way we're training, it's exposing you to a lot more situations where you have to make those passes and those decisions, and I think it's really setting us up to play good, entertaining rugby."
And while he's enjoying the new brand of rugby, he says some games have to be won by rolling up the sleeves and going back to basics.
"I think it's very important to front up physically as well. You don't want to be throwing balls out the back on every carry, it will be a good bit of just knuckling down and biting the bullet, putting the head down and carrying forward, building momentum off the back of that."
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