Koeman left his post as Holland coach to take charge after Barca had sacked Quique Setien.
Agent Rob Jansen said: “You have to realise: Ronald had already rejected Barcelona twice.
“This was the third time. Twice before he was firm and said he couldn't take it. If he had said no, it would be over. Then they would not have come back."
Koeman also recalled: "Everyone thought it was a shame (leaving Holland).
"I also thought it was a shame, because there was a really good click with the group. But if you work in football you have to be selfish from time to time. But that was discussed with the KNVB when I became national coach. This would not have been possible without a clause. Everyone understood it, even within the union.
"Being a national coach is great, but nothing can be compared to being a coach at Barcelona. It had to be that way. Some things are directed, I really believe in that."