The Irish flanker said the team was over-trained ahead of the first test, which the All Blacks won 30-15, and the drawn third test.
"To be honest, I'd be pretty critical of it because I think we should have won the tour and we probably should have won it comfortably," O'Brien said in an interview with OffTheBall.com.
"There's the best players in the world on a Lions tour. I know you are playing the best team in the world, but with the quality and strength in depth we had we probably should have won the tour. It wasn't down to fatigue. It was probably management a bit, in terms of how our weeks went."
"The first week, we definitely over-trained on the Thursday and maybe the coaches were panicking a little bit about getting the information into us," O'Brien said.
"On the first week [of the first test], we had a triple [session] day, [the] lads' legs were heavy on the Thursday and we were playing the All Blacks on Saturday.
"We did nearly a similar thing in the last week. So maybe it's more [from] a coaching point of view, in terms of taking lessons."
O'Brien played in all three tests including the victory in the second test in Wellington.
Photo by: GETTY IMAGES (Caption: Sean O'Brien says the Lions were over-trained ahead of the first and third tests against the All Blacks)