Plato identified the problem with observation in his allegory regarding shadows on cave walls. Modern arguments against naive realism can be found in the philosophy of science literature. Note that not all observations are unreliable. Observation can still inform us about the world. We make a mistake if we think observations are unbiased, but we make an equally onerous mistake if we think observations are irrelevant to knowledge.
Observations often depend on theory.
Facts are theory-laden. However, note that such observations don't need to be theory-independent in order to be reliable. For a non-musician who doesn't read music, it might take many months of study to be able to develop the theoretical baggage necessary to make this observation. This does not mean that the observation is purely an artifact of the observer. No evidence is absolutely reliable, and, arguably, no evidence is theory-independent.