Deterministic situation means such situation in which every aspect is known and can be determined accurately. There is nothing uncertain in it. Such situations are also called Situation of Certainty. For example:
If there are two toy cars. One moves at a speed of 20 miles per hour and the other moves at a speed of 30 miles per hour. If both the cars start moving for same destination at the same time on same route, which one will reach the destination first? It will always be that car which moves at the higher speed i.e., 30 mph in this case. This is certain.
But we may have some doubt about the toy cars. They may have some breakdown rate. There may be some unknown reasons that may affect the speed. These bring uncertainties in the situation. Still, one need to get some quantifiable understanding about these uncertainties. We may start talking in terms of chance or probability. Such situations are called Probabilistic Situations or Situations of Uncertainties or Stochastic Situations or Risky Situations.
Suppose you eat one Samosa on Monday, Wednesday and Friday, two Samosas on Tuesday, Saturday and Sunday, and no Samosa on Thursday, but you do it with certainty. It is a deterministic situation even though the number of Samosas you eat in a day varies. There is no element of uncertainty here. But, if you are not sure about how many Samosas you would eat in a day as it depends on your mood and also the taste of the Samosas, uncertainties get into the situation. For a Samosa vendor, the number of customers arriving during various time periods and their consumption pattern of Samosas are somewhat probabilistic.
We have some level of uncertainty in almost all the situations in real life. High level of uncertainty provides discomfort in decision making. That's why various measures are taken to reduce the uncertainty and move closer to deterministic situation. Automation, training the employees, bringing experienced consultants in important projects, implementing standard procedures etc. are some of the common measures taken to reduce uncertainties and move closer to deterministic situation.