We believed our own hype.
Perhaps we couldn't keep Koeman; but we certainly believe that no player or manager is irreplaceable thanks to our savviness and ability to find unappreciated gems in the transfer market.
Of course, the reality is that misses are as common as hits in the transfer market, even for clubs with the best recruitment records and players with far more pedigree than the ones we typically target and recruit.
It doesn't take many misses for things fall out of sync and the squad to experience a dilution in quality, especially when you're almost entirely reliant on transfer proceeds for (re)investment.