When we are having a performance problem with one of our staff in a certain position the easy thing to do is to keep investing in more training and development and hope for the best. If you can see steady improvement, by all means keep going. You likely have someone with aptitude who just needs more training.
If, on the other hand, improvement seems slow and painful, you need to be careful. Many people I talk to operate on the assumption that anyone can do anything with enough patience and training. It is true that most people will improve over time with training, but there is another subtle truth worth understanding.
People with high aptitude for certain tasks will improve much quicker than those who don’t.
The result being, that over time and with more training, the gap between your high aptitude staff and your low aptitude staff will widen. The high aptitude people simply learn faster.
This is the reason the air force washes out so many potential pilots as early as possible. With so many hopeful candidates, they pick those that have the highest aptitude for the work as early as possible. Since millions of dollars are going to be invested in each pilot, they want to know they are picking someone who will learn quickly and have a high probability of success before they invest too much.
Motivationally, it can quickly become a disaster when we keep encouraging someone to train and develop their skills; meanwhile they are watching their peers achieve more success with less effort.
When it becomes apparent that someone does not have the aptitude required for a position, we need to act for their sake, and for the sake of the organization. Acting means moving them to another position where you think they may have the aptitude to succeed, or letting them go from the organization.
Leaving them where they are and watching the gap widen between them and their peers is not fair to anyone.