By common consensus, top goalkeepers are a rare breed.
If we are often told that they are mad - occasionally on compelling grounds - it can only be because their playing position places them under greater psychological duress than anyone else on the field.
When a striker misses a chance, he can usually console himself with the knowledge that another opportunity will soon present itself. For the goalkeeper, there is no second chance. A split-second miscalculation can be the difference between glory and despair.
It should make good goalkeepers the most precious commodity in the sport, and yet on the transfer market they appear strangely undervalued. The only goalkeeper to feature in the list of football's biggest transfers is Gianluigi Buffon, who reportedly cost £32.6 million when he joined Juventus from Parma in 2001.
No other keeper comes close, making Craig Gordon one of the most expensive goalkeepers in the game's history despite only costing £7m (rising to £9m) when he joined Sunderland from Hearts four years ago.
It is not because nobody wants to buy goalkeepers, however, but because nobody is prepared to sell them. Goal-scorers and crowd pleasers may fire the imaginations of the fans and the media, but a reliable world-class goalkeeper is truly priceless. As a result, the game's elite net-minders rarely feature in the transfer gossip columns - and when they do, the fees evoked can be astronomical.
Replacing a proven goalkeeper is therefore one of the trickiest tasks any top-level club will ever have to undertake.
David de Gea's uncertain start to his Manchester United career has quickly been seized upon by the media, and there are clear parallels with Bayern Munich's struggles to find a long-term successor to Oliver Kahn.
Louis van Gaal paid with his job after deciding to place his faith in 22-year-old Thomas Kraft mid-way through last season. Having impressed during Bayern's winter training camp, the home-grown player was thrust into the first team by van Gaal but a series of uncertain displays - culminating in a costly blunder in a 1-1 draw at Nuremberg - saw van Gaal's authority eroded so completely that he was shown the door.
Caretaker coach Andries Jonker promptly returned the number one jersey to 36-year-old veteran Hans-Joerg Butt and Kraft agreed to join Hertha Berlin before the season was out.
Modern media coverage means that there is no hiding place for young goalkeepers like De Gea and Kraft, with pundits, newspaper columnists and bloggers crawling over each other in their haste to identify a failed signing by a top-rank club.
Where once blunders by up-and-coming keepers could be written off as inexperience, the timeframe for adjustment to life at results-obsessed Champions League sides is getting narrower by the season. Given the huge psychological demands that accompany football's loneliest position and the fact that many goalkeepers continue to develop until well into their 30s, it is slightly surprising that clubs of United and Bayern's stature are even prepared to take such gambles on goalkeepers who are yet to reach professional maturity.
An interesting experiment in goalkeeper development is currently under way at Corsica's Stade Francois, home to Ligue 1 newcomers Ajaccio, who pulled off one of the coups of the transfer window by signing Mexico international Guillermo Ochoa.
A star in his homeland with Club América, Ochoa looked destined for one of Europe's heavyweights until a positive test for clenbuterol in the build-up to the CONCACAF Gold Cup scared off would-be suitors and enabled Ajaccio to pounce.
Seeking simply "to make myself known and launch my career" at Ajaccio, the 26-year-old earned a handsome share of the French sport headlines on Saturday with some jaw-dropping reflex saves in a 1-1 draw at Lyon.
Ochoa's arrival at Ajaccio may have owed to regrettable circumstances, but De Gea would surely envy the comparative tranquillity of his working environment.