Jurgen Klopp says he watched footage of alternative signings to Virgil van Dijk "500 million times" before deciding they were not good enough for Liverpool.
The centre-back was heavily linked with a move to Anfield in the transfer window but Liverpool's interest ended after Southampton threatened to report them for making an allegedly illegal approach for the player.
Klopp signed full-back Andrew Robertson from Hull City but did not otherwise strengthen a defence that has looked far from convincing in the early weeks of the season.
Liverpool, down to 10 men, shipped five goals against Manchester City last week before letting a lead slip to draw 2-2 with Sevilla in the Champions League on Wednesday.
But Klopp has hit back at suggestions that he did not consider alternatives to Van Dijk, insisting the players he watched would not have improved his side.
"We watched all of them 500 million times, but what if the new player doesn't hit the first ball and he makes exactly the same mistake?" he said.
"It is not that we ignore it. I said if there would have been a solution out there, we would have done it. I had to make a decision and the decision was our boys are not worse than them."
The Reds begin their Burnley preparations... pic.twitter.com/3drXU5GHeK-- Liverpool FC (@LFC) September 14, 2017
Klopp also dismissed suggestions he is too lenient towards players who have made costly errors during matches.
"I believe in trust," said the 50-year-old, whose side host Burnley in the Premier League on Saturday. "I trust people until they give me an opportunity or a possibility not to trust them anymore. That's how I understand life.
"My job is really to make the best out of this season and it's easy for me in a lot of moments to believe in this team - it's easy.
"Oh yeah, sometimes they make bulls**t, and we are not happy. Sometimes [there are] goals I'm angry about, and it's not the first one. Of course, you wish we could have done [things] differently, but that can happen.
"Really, with all this about [our defenders], go out there and ask other teams whether they'd like to pick them. You would be really surprised.
"Let's say when I came here we started new and now we have this team. When I came in, we were ninth and now, 'oof'. We are really on a good way.
"Sometimes we make mistakes because we are offensively that strong."