For Aaron Mokoena, it has caused sleepless nights.
For Pompey fans, it has provided extremely uncomfortable viewing.
For Steve Cotterill, it is giving him the headache from hell as he racks his brains attempting to come up with a cure.
The Blues' defensive frailties are a worry that just won't go away.
Clearly they have applied the brakes to what a month ago had emerged into such a promising campaign.
A total of 12 goals conceded in the last four matches have left Steve Cotterill's side glancing nervously over their shoulders towards the relegation zone.
That and the little matter of an FA Cup humiliation at Brighton.
On the pitch, Pompey's defensive problems have been there for all to see, especially over the last three weeks.
Mokoena has been joined at various times by Ibrahima Sonko, Ricardo Rocha, Greg Halford, Joel Ward, Carl Dickinson and Hermann Hreidarsson.
Yet still the goals continue to flood in.
Inevitably, it has prompted extra attention on the training ground in recent weeks as Cotterill and his coaching staff look to create a defensive resilience.
And Mokoena admits the on-going problem is weighing heavily on his own shoulders.
He said: 'I normally get frustrated and have sleepless nights if I lose a match or if I concede a goal.
'The defending is a great concern, it's absolutely a great concern.
'We always emphasise the fact that it is unacceptable. We need clean sheets just as much as we need to score goals. We need to defend as a unit.
'We are working on that in training and watching videos as well so we are raising that factor quite often.
'You don't just defend with two centre-backs.
'What we have worked on in training is also pressing the ball, which is part of defending.
'It depends where the ball is, our distances as a team, it's so many things which are a factor.
'To score a goal can be one player but we have got to work together as a team to get into the box to score that goal.
'The same can be said for keeping a clean sheet, defending can be about a defensive error or individual mistakes but we defend as a team. It's important that we understand that.
'As much as strikers are more expensive than defenders, I believe defending is harder so we must work together.
'It's a great concern and in the second half of the season we need to rectify that and do better.'
The latest defensive capitulation was against Brighton last weekend.
For the second time in their past three matches, Pompey finished the game with just 10 men.
Nonetheless, despite the numerical disadvantage, the defending has unquestionably been poor over the past month.
A 3-3 draw at Leeds was followed by a 3-0 defeat at Watford on New Year's Day.
They then suffered an unwarranted 3-2 Fratton Park defeat to Hull.
The 3-1 loss at Brighton continues that dreadful defensive run, much to the annoyance of supporters.
But Mokoena has refused to become involved in a blame culture.
He added: 'It's not about pointing fingers, that is not what we want in the dressing room.
'People can do that but not in the dressing room.
'I always try to motivate myself and the boys by drifting back to the games that we won.
'It gets to a point where what do we do as a team? Do we dwell on that? Do we judge ourselves? Or do we work harder?
'It's all about coming back stronger and that is what we are trying to do.'