Yes, true!

However, often even before going to the subjective interpretation, you need some sources to base this on. Just think about the fact that much of what we know about history is based on a very limited number of sources. It gets better with the modern era, but for the times before that we really are quite limited. I had been thinking about this for a while. Imagine if in the future, historians had only my writings to base their interpretations on. Or the writings of some one other person. So the sources themselves might be biased or wrong.