I doubt it’ll be a one-off. That’s quite a young team Klopp’s built tbf. Doesn’t matter how much their rivals spend, they’re going to take some pegging back, especially if they ever get a genuine playmaker in midfield (imagine Liverpool with Kevin De Bruyne)
That's the thing. Players pick up injuries, grow a year older or just can't be bothered after winning everything. For every messi theres a ronaldinho.
Also players who have clocked up a lot of miles sometimes lose it. Just look at rooney, his body was finished at 28.

