In the barnstorming days long before his current club malaise, it was widely accepted that Wayne Rooney's most effective moments were fuelled by rage. Every wild swipe of the ball or furious pursuit of a referee were tolerable by-products of his nuclear temperament.
Diego Costa's contributions to the ailing Chelsea cause appear to be toiling under a similar assumption. At his most combustible, Costa epitomises the simmering near-chaos of a Jose Mourinho side in defeat: a series of ill-tempered vignettes, a gradual loss of focus and, like a snake chasing its own tail, injustice and frustration feeding on each other until the game is gone.
Quite simply, how useful is Costa when bee meets bonnet? On a scale of zero to Marouane Fellaini's elbows, the effectiveness of his aggression registers at less than half a Pepe. Somehow this season, despite the gleeful (and now premeditated) provocation of opponents and supporters, Costa has avoided a volcanic explosion of rage, releasing his fury in irritable bursts.
Rather than a red card and a three-match ban, the 26-year-old Costa is earning himself the more drawn-out punishment of soul-sapping ironic cheers every time his hold-up play comes to nought. It's not a million miles from the sort of ritual humiliation that befell Fernando Torres once everyone realised he'd become a figure of footballing pity. Costa has enough about him not to plummet that far, of course, but opposition schadenfreude is a tough nut to crack when your team is in poor form. It's a virtually indestructible one when you're distracted by the prospect of another bout of violent posturing.
A more generous comparison would be to Didier Drogba. He experienced peripheral dramas at Chelsea before proving his eternal worth, but his high-yield bullying of defenders extended way beyond Costa's repertoire of permanently cocked, battle-ready arms and provocative mini head-nods toward enemies. Drogba's was an altogether more fruitful form of footballing aggression, as he barnstormed his way through the hearts of defences.
In contrast, not a single Costa goal for Chelsea has been carved out that way. Well-timed, arcing runs behind offside traps. Crafty backsteps around the 6-yard box to meet low crosses. Perfectly placed headers. None of these are particularly muscular goal-scoring art forms. All surely benefit from a clear mind.
The World Health Organization probably has more important fish to fry than to finally explore the epidemiology of Second Season Syndrome, but Costa is showing some acute early symptoms. When attempting to follow up an impressive debut season, the fear is of being "found out." Based on the cross-section of Premier League experiences upon which to judge him this season -- and, admittedly, the sample size right now is four league games, in which he has one goal and one assist -- Costa's opponents have satisfied themselves with his most obvious Achilles' heel: wind him up and watch him go.
In Chelsea's self-inflicted adversity against Swansea, hopeless mayhem at Manchester City, rain-swept warfare against West Brom and fragile calamity at home to Crystal Palace, Costa was almost instantly met with defenders who had done their elementary homework. Claudio Yacob and Damien Delaney (the latter describing Costa as a "good ol' fashioned bruiser") even received a semi-congratulatory Costa embrace for their efforts. Honourably old-fashioned as this looked, it suggests that he accepts such pumped-up pantomime as part of his game.
Almost as likely as him hitting a century of goals over the next few seasons and etching himself into Chelsea's modern history is the prospect of the club trying to offload a hamstrung, burnt-out 30-year-old on loan back to La Liga. Such risks are part of life at the top of the transfer food chain, especially when fans yearn for a player to be firing on all cylinders at 21 rather than finding their Premier League feet at 26. Drogba needed two seasons at Stamford Bridge before showing his best form and peaked at the age of 31 in his sixth year at the club. With the shelf life of elite-level strikers as short as it is, Costa doesn't have that much time to waste on twice-weekly wars with willing and able centre-backs.
With John Terry battling the latest question marks over his physical top-flight capability, title-winning dependables like Cesc Fabregas and Branislav Ivanovic looking particularly dishevelled -- as if they'd aged three years in the space of a summer -- and Eden Hazard yet to click into top gear, Costa is the strongest vertebra in Chelsea's uncertain spine. There's nothing to suggest that a focused, unshakeable Costa wouldn't be more potent. That's surely what the £32m was paid for.
Take the aggression out of his game and Costa might well be twice the player.
Adam Hurrey is a London-based football writer and author of the book "Football Clichés".