I can only assume that you weren't around to see Paisley at work. These aren't my words, but are spot on:
"The greatest strength of Bob Paisley, though, had to be his ability to sign the right players for his team, allied to an excellent sense of when to let existing players go. Not only were his signings on balance the best of any Liverpool manager, but he never kept a player past his sell-by date. Unlike Shankly, Paisley was ruthless when it came to letting older players go. He didn’t enjoy the process, but he didn’t let any sentimentality cloud his judgement."