Physicists frequently analyze a physical situation starting at some moment in time, and ignore what happened before that moment in time. To do this, however, they need to understand what was happening at that initial moment. That is, they need Initial Data. This is very similar to using Boundaries, which requires having Boundary Conditions.
Now, here, you see, it takes all the running you can do, to keep in the same place. If you want to get somewhere else, you must run twice as fast as that.
The Red Queen in Lewis Carroll's Through the Looking Glass