The concepts and methods in many subjects, particularly Mathematics and the other sciences, tend to build one upon another. If an idea is missed or poorly understood, the concepts which follow are more difficult to grasp. Confidence is easily lost and it is all too easy to believe the subject will remain a mystery. Most of us have experienced that kind of downward spiral at some stage.
In one-to-one lessons, it is possible to observe the mistakes and identify the concepts which have not been understood. This is very important since most students are largely unaware of the gaps in their understanding. Once the problem areas have been identified, it is often straightforward to provide the remedy through careful explanation and practice.
As problem areas are resolved, a student's confidence grows and they usually begin to realise that the subject is not as difficult as they imagined.