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 mental noting or acknowledgement in 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 keep acknowledging after doubt has arisen. We are taught to treat doubt just like any other condition of the mind which has a beginning, a middle and an end. We need to direct the mind to acknowledge that doubt has arisen and then gently bring the mind 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 some future condition that may or may not occur. If the mind is in the present moment with acknowledgement 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, there is a good foundation for the future. Consequently, we should practice confidence in the present moment by acknowledgement instead of following doubt.