As a concept, uncertainty deals with the idea that any outcome cannot be guaranteed. We may choose to believe that we are certain but in reality the uncertainty of everyday decisions is clear. If I bounce a ball off a wall, it will most definitely bounce back. At least, that is what we expect. The issue here is not necessarily the outcome being possible or not, but the feeling of uncertainty and doubt itself. These feelings bring anxiety and stress that is almost always unnecessary.
Accept uncertainty, accept the doubt and uneasiness, and let is pass. That is what I believe one should do to be able to overcome this type of anxiety. At least this is one way it can be dealt with. Another option can be to somehow guarantee an outcome by thinking of all possible scenarios which is not always possible. Calmness and acceptance is the best possible solution. Instead of controlling the exterior and the world around us, we can control ourselves, our reactions at first and then slowly work to control our expectations and feelings of uncertainty.
Positivity is always possible. Adversity and conflict are inevitable. The power within is mostly greater than you think it is so utilize it, nurture it, and get control of it.