Many things can influence the way your employees perform.
When performance is good it is usually attributable to many factors, a good mix in all areas. So, outstanding performance depends on all appropriate positive influences being present
Poor performance works in a different way and can be caused by just one factor that negatively impacts effectiveness. Often, performance problems that go unchecked will get bigger.
Influences on performance -
A person may have an innate ability when it comes to certain activities. Poor performance may simply be caused be a lack of aptitude. If you are placing emphasis on an employee to carry out tasks he is not best suited to you are getting negative results from his weak points rather than using his strong ones to your benefit.
Skills can be acquired, unlike aptitude. Just because someone does not have the skill to do something does not mean they cannot be taught. Poor performance may happen if someone is not trained to do their job.
Employees need to have a clear understanding of their responsibilities and exactly what it is that is expected of them in order to complete them effectively. Lack of good communication in this area can lead to unsatisfactory results.
Intermittent lack of motivation
Motivation is the key here. Several things can affect a person's motivation. Some may be related to things outside the workplace and things within it. An employee who usually delivers who gives a poor performance may be temporarily lacking drive.
Permanent lack of motivation
An employee who persistently performs badly is harder to cure. If performance consistently poor it is unlikely to be rectifiable.
If someone in your employment is failing to persist with their projects it might be that they lack confidence, feel overburdened or unsuited to the task. Many of the above factors could play a part here.
It is vital that performance issues are addressed with expedience. Most problems can be dealt with once you know the causes. Changing the way tasks are communicated to employees will help those whose poor performance is due to lack of clarity. Getting to know the strong and weak points of team members will help you assign tasks to those who are most suited to them. Sometimes a lack of resources or even lack of the correct tools may be prohibiting an otherwise apt worker from carrying out their duties to a high standard.
In a smaller company it may be easier to have your finger on the pulse, so to speak, but larger corporations need to find ways to operate that mean employees don't become invisible or part of the machine. A one to one talk always reaps better rewards than an impersonal email.
Managers who want to avoid performance problems should touch base as often as they can. An approachable boss is more likely to hear direct from his employees about any struggles they are having. It's far easier to prevent performance problems than to cure them, although fixing things after the fact is possible.