In the beginning, many individuals start their workout routines without a solid plan, just a rough goal in mind. These goals may be to lose weight, build muscle, increase endurance, run a marathon, or anything else that may be out there. As different as each of these goals may be, they all have one thing in common: there is no single route that leads to success in achieving them.
Look at how runners train for a marathon. Do runners simply run 3 miles a day in hopes of achieving their goal? Of course not. They may start out this way to build up their endurance but as their workouts progress, they push themselves farther. As a matter of fact, many alter the distances they run day to day. One day may be a 5 mile run and another may be a 15 mile run. By altering the distance, they continuously train their bodies to evolve and adapt, making them more efficient runners.
The same can be set for weight lifters. One of the most common introductory programs is the standard 3 sets of 10 repetitions for a specific muscle group. There is nothing wrong with this approach as everyone must start somewhere but once you are acquainted with the exercises and your muscular strength/endurance has improved, it would be wise to up the intensity. Some start by adding a 4th set to the mix, others increase the weight, some incorporate specialty weight lifting methods such as pyramids, tear downs, chains, negatives, and a variety of other techniques. The point is, without changing the pattern, the body will not grow and become less responsive to the exercises.
Regardless of your goals, if you feel that you have reached an plateau and cannot seem to achieve the results you are looking for, alter your workout and change things up. Do something you wouldn't normally do and you will be amazed at the success you find.