Saido Berahino thought giving the ball away for Cardiff's dramatic equaliser in last Saturday's 3-3 draw was bad enough in costing West Brom two points.
But the stoppage-time mishap caused something far more destructive in the Baggies' camp.
Team-mate James Morrison reportedly punched the 20-year-old in the dressing room, making a poor situation much, much worse.
In times of difficulty it is vital everyone at the club sticks together to keep morale high. This stupid reaction to an honest mistake will have caused a divide within the squad.
Players will be consoling Berahino or leaving the youngster alone to dwell on the lowest point of a promising career.
The England U21 international scored a fabulous winner against the champions Manchester United in October, and was linked with getting an England call-up after scoring six goals in five U21 appearances.
This superb start has been forgotten after West Brom's slump since sacking Steve Clarke, and the dressing-room altercation is the only reason Berahino is now making the headlines.
On Sunday, the day after the damaging draw against Cardiff, Berahino said sorry to the fans on Twitter: "Apologies for my mistake, cost the team the three points."
Unfortunately, an inexperienced football is likely to respond badly to his negative publicity, compounded by some classless abuse on Twitter and allegedly by a senior colleague.
Morrison is the real villain here, and coach Pepe Mel must discipline the former Middlesbrough midfielder if he wants this unsavoury issue to be resolved.
Whether West Brom are relegated or not could be irrelevant to Berahino, as he may have to leave his boyhood club because of another's irresponsible actions.
There won't be any shortage of interest in a talented forward who has been a revelation in the West Midlands, so Premier League clubs are sure to bid this summer.
On the other hand, Morrison may find it more difficult to better his career if the rumours are true.
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