The difference between success and failure is often the ability to continue to work hard in the face of adversity. When it comes to meditation practice, we define success in the extent to which a person has reduced the mental defilements of greed anger and delusion. According to the Buddha, this can be achieved simply by bringing the mind to the present moment on a continual basis.
However, while the the instructions are simple, the practice is sometimes difficult. This is often because the student lacks the confidence necessary to bring the mind to the present moment after doubt has arisen. We are taught to treat doubt just like any other condition of the mind which has a beginning middle and an end. We need to direct the mind to observe that doubt has arisen, observe its qualities, and then gently bring it back to the present moment.
Once returned to the present moment, we can see that things are ok in the here and now and the doubt refers to a fear of some future condition that may or may not occur. If the mind is in the present moment and we are grounded in the five precepts of not killing, not stealing, not committing adultery, not telling lies and not using drugs or alcohol, we can be certain of a good future so there is no need to follow doubt. Consequently, confidence in the present moment can be relied upon.