Here are some principles in planning. Forecasting can use numbers or judgment. Trend lines are fine, but so are scenarios. If your organization has confidence in quantitative forecasts, use them. If your people are more comfortable with non-statistical forecasts, do them.
Many people think of the future only one way.
Planning, however, must be dynamic. Betting on one technology, for example, closes off other futures, some of them more likely. People are always overconfident about technology. Doomsayers make great copy, but we don't believe them. We invest our hopes in the newest inventions and scientific breakthroughs.