Past performance doesn't guarantee future results, but the results/output are a direct product of the input (cultural factors, economic ones, etc.). Couldn't we

Past performance doesn't guarantee future results, but the results/output are a direct product of the input (cultural factors, economic ones, etc.). Couldn't we say that past performance is a great indicator of future results as long as there hasn't been a dramatic shift in input that we can identify? If there's been such a change in a factor that would cause a substantial difference in the trend, what would you suggest it is?