The Uncertainty of Predicting or Knowing Something will happen but not When.

Predicting the future is difficult, even if you know the technology. Take the example of flat screen televisions. While they existed in the 90s, it took 15 more years for them to become commercially viable. The problem was the yield of properly functioning pixels. Similar challenges exist in predicting the timelines for general purpose robotics, molecular computing, and advancements in medicine. Sometimes, the timing depends on coincidences and personal circumstances. It's easier to say how things will end up rather than when they will happen.