Many business people and managers are spending too much time trying to change underperforming people who work for them. They seem to believe that if they train people - tell them what to do or even threaten them with sack - then performance level will go up.
The successful manager concentrates on developing strengths of his team members - not trying to correct their weaknesses. Sometimes you have to manage around a weakness, but you can't make people what they're not.
Some years ago I decided to improve my golf by taking some lessons. A friend and I spent some hours with a professional golfer and coach at a local country club. This was really useful to me and I did get better. However my friend Robin hadn't a clue. No matter what pro told him to do, how to change his stance and his grip, he could hardly hit ball.
If you'd given Robin a hundred lessons and threatened him with a gun, I doubt if he'd ever have completed a round of golf in less than two days. Robin is a successful lawyer and makes a lot of money, however a golfer - he is not.
So if you have a sales person on your team who isn't bringing in sales or a production engineer who isn't making his quota, then you have to make a decision. Is this person not producing because they don't have ability - because they need more training or - because there's another reason?
You can read more about coaching and other reasons for non performance in my book - "How to get more Sales by Motivating your Team" but for moment it's important to understand that individual may not be able to do job.
They may tell you they can do job because they're unwilling to accept defeat; however I've known people in sales jobs who shouldn't be in sales and doctors, plumbers, lawyers and engineers who were also in wrong job.
What you need to do is get people who can't do job into a job that they can do or get them out of your team.