They make educated guesses using past performance of the company.by watching trends,holidays,past sells projections,depends on what your business is.I guess you could look at it like farmers watching the weather to see if a storm is coming or just rain to either judge if they need to protect their crops or plan for a good growth/harvest of their crops from the rain.or watch for a dry season and plan on having a smaller crop that year.the manager may even have to watch it's customers to see if they are going to buy/purchase that year.in other words check their potential customer base for the year and try and predict if they are going ot buy at the same levels they did in the past.in other words knowing what mite effect your customers ability to produce what they did the years before which in turn effects if they are going to place orders with your business.what's that phrase the trickle down effect.just my guess.
