Swansea were more assertive and cohesive from the outset, exposing the United defence's vulnerability at set pieces twice in the first 10 minutes, when corners saw Gomis allowed two unchallenged headers, one of which was cleared off the line by Ander Herrera.
It can also be nihilistic: archness as a perpetual defence against the vulnerability of being sincere.
Their defence still carries vulnerability, and there can be no doubt they were grateful for a couple of decisions from referee Clattenburg that were greeted with commendable good grace by City manager Manuel Pellegrini.
Rodgers works on defensive organisation and is certainly too skilled and confident a coach to bring in an outsider to assist with defence, but that vulnerability must remain a concern.
Having won their last two games by narrow margins, Juergen Klopp's side looked more like the team that took a solitary point from their previous three, with little threat in attack and familiar vulnerabilities in defence.
Bayern again found the Champions League a different proposition as they struggled to break down a surprisingly cautious Arsenal in the first half of Tuesday's game and showed vulnerabilities in defence when the visitors came at them in the final half hour.
Germany had exuded their usual air of calm confidence beforehand but there was always the vague suspicion that it masked an uncharacteristic vulnerability in defence.
Jamie Vardy and Leonardo Ulloa were not the same threat that they posed to Louis van Gaal's defence and Leicester's vulnerability to set pieces was exposed.
Businesses employ Radcliffe, an expert in psychology, to use social engineering techniques to try to breach their defences and find their vulnerabilities.
It will not be that easy, of course, and there were moments when United's vulnerability in defence briefly seemed like a throwback to last season.
