When you see an egg there is no way to verify that the yolk is yellow in that egg before you break it; you must crack the egg to know for sure; without an act of knowing (i.e. experiencing the object) we cannot be certain. We can predict the yolk will be yellow based on previous experience but this knowledge cannot be guaranteed in the future; it is possible one day a green egg yolk will be found.
This is one of the limits of knowledge; we know only in the present. For example, the past of an object is still thought of in the present and expecting a future is also a present thought. Knowledge requires a knower and we bring the limits of our present to the object.
When you are diagnosed with Parkinson’s you are given a long line of eggs you have to break open and eat. It is very tempting to try and predict the next egg or the egg 101st down the line will have yellow yolk. It is simply impossible to know for sure what those eggs will contain: we can only approach the disease in the present.