Variables
Sometimes there are so many random variables that one needs to deal with all at once. It kind of gets on to your nerves.
Most of the variables are stochastic in nature. The distribution for each of these variables X(t) changes for each day. It looks as though X(t) follows a known distribution for a given t. However as t increases, one starts seeing the distributions are no longer stable. There are jumps / non random behavior beyond comprehension.