Most philosophers talk about justification of individual people, not of ideas or concepts themselves. This means that what may count as knowledge to one may not count to another. The subjective nature of knowledge is based in part on the idea that beliefs are things that individuals have and that such beliefs are either justified or not justified. When you think about this, it actually makes sense. Someone might have more evidence or different experiences than someone else, and similarly they might believe things that someone else doesn't believe or have evidence for something that they don't believe. Simply put, universal knowledge, which is something that everyone knows, can be very difficult to obtain. Truth, if it exists, is not like justification. The truth is universal. It's how people access knowledge, and it can vary