I think for us it's because the majority of big money signings we've made have come with the theory of the player hopefully being worth their fee in time, more so than already being worth it. Modric is probably the only one that ended up bettering (and some!) what we'd hoped. Lamela done well but wasn't worth the outlay of a record buy. Had we paid about £10m less I think we could've called him a true success story. Soldado was probably the one player who actually had the pedigree at the time to warrant the fee, albeit ended up being awful. Sanchez never reached his potential, did have one or two decent seasons but that was it. Ndombele see above but without the decent seasons. Lo Celso the same as fat boy. Richarlison was a shocker from the off as we paid probably twice his value and we've seen as such. Utterly bonkers signing that one. Johnson is yet to reach his potential. Solanke has a similar vibe to Richarlison, albeit we've probably only paid about a third more than his value instead of twice as much. Hopefully proves last season wasn't a one off, if he doesn't, we're in trouble.
And then there's the rest of the rogue's gallery Barren Dent was our joint-record signing at the time yet we didn't need (or want) him Paulinho was a damning indictment of the quality of defending in the Brazilian league David Bentley was another player we didn't even need Dean Richards was an arseache to sign (courtesy of a Reform Ltd MP...) and was permanently injured Helder Postiga was more of a bust than Sydney Sweeney
