It's a bit like criticising your own family. It's OK for you to do it, but not someone else.
Artur Boruc has been in the bosom of Celtic's family for more than three years now. The Scottish champions' support has afforded him cult status, a matter they would do well to rethink. Want to have a pop at the Holy Goalie? Then look out your bulletproof vest.
Boruc was not responsible for Celtic's exit from Europe on Tuesday night. Rather, an inability to beat such a mediocre outfit as Aalborg on two separate occasions proved their downfall.
Yet the goalkeeper was at fault as Gary Caldwell bundled in that late and fateful own goal in Denmark, having half come for and failed to collect a cross. It was the latest in a long line of aberrations this season, albeit far from the most glaring.
Arsenal and Milan are among those who have courted Boruc amid a string of outstanding displays over the last two years. His penalty save from Louis Saha, of course, was as pivotal as Shunsuke Nakamura's free-kick brilliance as Manchester United were humbled in 2006.
Recent months, though, have proved troublesome for the 28-year-old, just when he should be approaching the peak of his career. In the course of this season he has, in brief: been suspended from international duty after high jinks on a trip to Ukraine, supplied a Great Sporting Gaffes-type howler in an Old Firm derby, been warned for a one-fingered salute in said game, been pictured puffing cigars and downing lager when supposedly recuperating from knee surgery and generally looked less than comfortable at his chosen profession. Hardly worthy of hero worship from the stands.
An inauspicious showing against St Mirren on Saturday would have been cut short after 15 minutes, had referee Willie Collum correctly issued a red card for Boruc's attempts to engage Craig Dargo in a spot of kung-fu. The keeper's decision to charge 25 yards out of his goal in the first place, says much about his apparent state of mind.
Not that he has ever been a shrinking violet, of course. During his time at Celtic, Boruc has been pictured poised on a fence at a Warsaw derby and has fallen foul of supporters at stadiums such as Easter Road and Tannadice. In an Old Firm match at Ibrox, he meandered across the pitch with a Celtic flag at full-time; following the same fixture at Celtic Park he donned a "God bless the Pope" T-shirt which, strangely, has not been spotted since.
None of this would be of overriding concern if Boruc was on top form, repaying Gordon Strachan's unwavering public and private support for him. But he is not; and not, surely, appealing to those clubs who could offer him an exit from Glasgow now that European football is over for another season.
If Celtic have to refocus their efforts after Tuesday's embarrassment, the same applies to Boruc. One of the most talented players in Britain must return to making headlines for saves, rather than controversy. As it stands, he is worthy of criticism. It may even arrive soon from Celtic fans, but don't bank on it.
