The main reasons of uncertainty are:
- Spontaneity of natural processes and phenomena, natural disasters (earthquakes, hurricanes, floods, drought, frost, ice).
- Accident. When in similar conditions the same event results from unequally many social and economic and engineering procedures.
- Availability of contradictory trends, collision of interests. These are military operations, the international conflicts.
- Probabilistic nature of scientific and technical progress. It is impracticable to define concrete consequences of these or those discoveries, technical inventions.
- Incompleteness, insufficiency of information on an object, process, phenomenon. This reason results in limitation of the person in collecting and processing of information, with permanent variability of this information.
- Limitation, material, financial, labor, etc. resources at acceptance and implementation of decisions; impossibility of unambiguous knowledge of an object at the developed levels and methods of scientific knowledge; limitation of conscious human activity, the existing differences in social mental sets, estimates, behavior.
Availability of uncertainty considerably complicates process of the choice of optimal solutions and can result in unpredictable results.
On time of emergence of uncertainty are distributed on retrospective, current and perspective.
Need of accounting of a factor of time at assessment of cost efficiency of the made decisions is caused by the fact that both the effect, and costs can be distributed in time.
The costs, equal in size, which are differently distributed in time provide unequal useful result of this or that type (economic, social, etc.)