Cullen's men must address discipline problem ahead of derby grudge match
The loss against Glasgow last weekend was an untimely reminder of slipped opportunities earlier in the season.
The tempo set at the start of the game showed Leinster's recent resurgence and confidence in this Pro12 campaign but the inability to convert the opportunities into points was a reminder of the naïve, innocent and inexperienced days gone by.
Luke McGrath set the pace of the game early on and quick tap penalties kept Glasgow on their toes and showed Leinster's intent.
But Cathal Marsh's skipped pass showed a lack of belief in those outside him and also an inability to keep calm in the opposition defensive zone.
Both attributes will come with time but missing touch earlier clearly rattled him.
Marsh's progress has been exciting and has proved to all at Leinster that the future out-half berth at the province is secure, even with Ian Madigan's departure, and he will learn to forget mistakes and put them behind him for the benefit of the team and himself for the rest of the game.
Leinster will need to take this defeat on the chin and view it as a lesson of how not to play in the vital games coming up over the next few weeks.
They have made great strides climbing up the table during the international season and last week's glitch against Glasgow will pale into insignificance as they head for Connacht.
However there is a discipline problem that has sat within Leinster this season and while it seemed dormant for a while, as the defensive structure made the statisticians over-excited, this issue has raised its ugly head again.
Yellow cards are unacceptable in modern day rugby, while penalties are inevitable in the ebb and flow of a game. A team's reticence in giving away penalties is noticed by referees and their faith is generally put in the side with the better disciplinary record.
Leinster need to tighten up in this area as they have put in a lot of work into their defensive system. If they don't, there will be frustrating days ahead as the pressure comes on in the play-off games.
If, like this season, a squad fails at the ultimate goal of Champions Cup rugby, they get a second chance in the Pro12. For Irish provinces however, there's a third segment to the season and that is the inter-provincial derbies.
It's not as prevalent as in the past but there's much more at stake than just the all-important bragging rights. With a tour to South Africa coming up, these games are vital to pitch players against the players that know each other well both on and off the pitch.
Connacht and Leinster have had a tumultuous relationship in the past, and for a while the Westerners were almost a feeder province.
Connacht have a lot of pride at the Sportsground and the Leinster visit over Easter weekend will certainly draw a full house.
For Leinster, this game traditionally was a grudge match and the purpose was to silence the Westerners, reminding them of their place in Irish rugby, but Connacht's position at the top of the Pro12 table is not by accident.
While their performances have been impressive, the extra spice for them this weekend might send them over the edge. Leinster have to be very careful of this and must draw from their experience in all competitions this season.
Selection will be a blend of internationals that are available and those who have been keeping the Pro12 ticking over. Expect Connacht to pick their full complement of internationals while Leinster will mix it up.
For Leinster, winning tomorrow will prove they have what it takes to win the Pro12 while maintaining their provincial status in Ireland. The key is picking the right 23 and using them wisely for the 80 minutes.