Most individuals that participate in a training program are dedicated to tracking their progress throughout the program, which is generally monitored by strength gains. Many will find that increases in strength are easy to come by during their first couple months that they participate in a training program - whether that be for athletic performance, bodybuilding, or powerlifting. However, many of these same individuals will become frustrated when the progress begins to slow down, and eventually, in some cases, plateau.
Many athletes can become discouraged by this, however, it is important to keep this in mind; this is not a bad thing, it just means your body has adapted to the current training program you are partaking in. The beginner gains that your body has made have come from increased muscle fiber size and learning new movement patterns/becoming more efficient in those patterns. It is anticipated that athletes will hit this plateau at some point, and it is at this point in which exercise variability becomes important.
At this point, a strength & conditioning coach will make appropriate adjustments to the athlete’s training program. This may mean progressing the athlete's movements to a more advanced movement pattern, if it is safe to do so, or modifying the rep scheme that the athlete performs, usually meaning a higher intensity (heavier weight, lower reps). However, this can also work the opposite way, swinging the athlete into a hypertrophy phase, in which case they would be doing moderate intensity lifts with a higher rep scheme. These are just two of many tools that can be used to push an athlete through a plateau.
It is important to periodically modify your training program, as well as communicate with your coaches about your progress, and how you are feeling as an athlete. Plateaus will happen from time to time, however if you are having trouble breaking through that next plateau, it may be time to evaluate your training program as a whole, and make the necessary adjustments.