If you are strength training correctly and allowing enough time for recovery you should come back stronger each workout; most people will see real improvement for at least the first two years. In order to have real improvement it is necessary to have an accurate measurement to see if what you are doing is working, and if not make adjustments.
In the weight room counting repetitions is often used to measure improvement. Counting reps will measure improvement if form is adhered to, but often it is not. As an example, say you keep getting eight repetitions of an exercise, and you can't do anymore. You subconsciously cheat just a little to make the exercise easier. You lock out between reps, you swing you body into it a bit to get momentum, you shorten the range of motion just a tad to get that extra rep. Even with a trainer this often happens, as the trainer is anxious to see your continued improvement.