Redknapp had been confident about signing Hooper after Celtic finally accepted an offer from QPR, but the deal dragged on when the west London club failed to agree personal terms.
Norwich seized their chance to hijack the move and agreed a £5.5m fee with the Bhoys before securing Hooper's services on a four-year deal.
Redknapp admits that QPR took far too long to complete the switch and hopes a lesson has been learned as they approach other targets ahead of the new Championship campaign.
He told Sky Sports News: "You can't hang about. I could write a book about players that I have signed and lost over the years.
"Deals have got to be done quickly and it dragged on probably two-and-a-half months altogether that deal. It was miles too long.
"It should have been done, but that's how it goes, we learn from that one and move on. We can't make that same mistake again.
"If we're after a player and we really want him and he wants to come. Because the boy wanted to come, I don't care what anybody says, he was coming to us, but I just think that it seemed to be a bit of a mix up with the deal and everything. Never mind that's how it goes."
Redknapp was speaking after QPR rounded off their pre-season campaign with a 3-1 victory over Southend on Friday night
Andy Johnson, Stephane Mbia and Nedum Onuoha grabbed the goals for QPR, while it was a Clint Hill own goal which had briefly drawn Southend level.