Training meditation is, to a large extent, training concentration. A simple meditation exercise is to imagine a geometric figure and try to keep that image present without getting distracted.
In very brief moments we will inevitably get distracted. The distractions that arise will be of one of these three types: physical, emotional, or mental.
A physical distraction can be, for example, that the knees start to hurt, the back gets tired, or the neck bothers us. Physical sensations that take the focus of attention that we were trying to maintain on a certain thought and bring it towards the body.
An emotional distraction is a little more subtle. For example, we may feel anxiety or boredom. Perhaps a feeling of sadness surfaces. Or if we had a bad day and we are in a bad mood, it becomes difficult to direct attention towards the object of concentration.
Mental distractions are thoughts. We remember something, we start thinking about something else. We make associations. We direct attention to memories of the past or projections of the future.
To reduce these distractions and advance in meditation training, all these aspects (physical, emotional and mental) have to be worked on. Performing a comprehensive work of the individual is crucial if we want to obtain true results with this technique.