Think it was a terrible back pass which led to a goal? Which he apologised for to be fair.
Just a few others I remember, we were 3-1 up against Leeds and his individual errors led to them hauling it back to 3-3. He gave away a penalty at Anfield when not tracking Salah properly which led to another loss.
Ultimately, in my opinion, these errors add up and the lost points accumulate though.