Jamie Heaslip's try proved decisive, while Shane Jennings also scored for Leinster, as Ulster could only reply through six Ruan Pienaar penalties.
It meant that despite finishing at the top of the table following the regular season, Mark Anscombe's men were unable to lift their first title since 2006, leaving Best dejected.
"We made our plans fairly clear at the start of the season that we wanted to win something - anything else was going to be a bit of a failure for us," said the Ireland international.
"As per usual with our boys you couldn't fault the effort, just at times we lacked a bit of accuracy - our discipline was very poor.
"When you play top sides in finals that is going to be the difference and ultimately we feel we gifted them nine, maybe 12 points, and we lost the game by six so it probably sums up how good a team we are.
"It shows how good Leinster are if you give them half a chance - first half they had four visits to our half and come away with four scores. It's hard to take but you have to give them credit, but it doesn't make it any easier for us.
"It comes to a point where you have to stop learning (from defeats). Obviously you want to be learning and getting better but come big games we can't keep saying we need to do this and that.
"We probably got played by a team a lot more streetwise at the breakdown. I don't think they infringed any less than we did they were just smarter about it."
Despite missing out on initial selection, Best is now a candidate for a call-up to Warren Gatland's British and Irish Lions squad after England hooker Dylan Hartley was hit with a ban for being sent off in the Premiership final for Northampton Saints.
But the Ulster no.2 is adamant he remains focused only on moving on from this defeat.
"At the minute we are focused on Ulster," said the 30-year-old. "It is heartbreaking we have lost this game and it is hard to focus on anything else.
"Anything else is a bit of a sideshow at the moment. We have not just 23, but 35-40 hurting boys plus our management and that is what we are focusing on at the minute."
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