My take on our GK situation.
The difference between the two is that Mignolet simply can't do what we want from a keeper. Whereas Karius might be able to, but simply hasn't so far.
Currently Mignolet is better than Karius. He saves Sane's shot for me.
But, we know all there is to know about Mignolet. Good, bad or indifferent. This is his level. Adequate to win most games. But more likely to turn a win into a draw/loss than to make a match winning save. His movement off the line and distribution are not good enough. His feet are so slow. A number of times there are balls where I expect him to reach first, that he turns into 50/50's or narrowly wins the race but gives the opposition possession deep in our half and adds unnecessary pressure on the defence.
When Karius was bought I thought we were buying a confident keeper who would be on the front foot, sweeping up behind the defence, recycling possession and starting attacks with his quick distribution. Not the finished article by any means, but a keeper who was trying to do the right things.
Some people have already seen enough to decide he's not good enough now, and he never will be in the future. On the first point you'll get no argument from me or anyone else, he's clearly not been good enough. That's why Klopp had to go back to Mignolet.
On the second point I'm not so sure. I believe Karius at his best could be good enough. The problem for those of us who haven't completely written him off yet is that there is only one way to be sure. That's a consistent run of games being tested against all types of opposition in various situations.
I think Klopp is thinking along the same lines. He's unlikely to get a top quality keeper before the summer. So he either sticks with Mignolet, who he has already decided isn't good enough, or plays Karius.
Karius has until the end of the season to prove to Klopp that he can show those attributes that convinced Klopp to buy him in the first place. It's a risk that, at best, provides us with a solid No.1 who fits Klopp's system. But at worst, could cost us a champions league spot.