Why is documentary evidence often considered more reliable than witness testimony?

In the context of law, documentary evidence is often considered more reliable than witness testimony due to the inherent limitations and potential for error in human memory.12

While documentary evidence is frequently treated as superior, witness testimony has historically been viewed with a degree of suspicion. This skepticism is supported by psychological research demonstrating that memory is not a perfect recording of past events but rather a reconstruction. Eyewitness accounts can be degraded or distorted by external factors, such as exposure to misleading information or the influence of suggestive questioning, which can lead to the creation of vivid but incorrect memories. The fallibility of such testimony is underscored by cases where individuals were wrongfully convicted based on eyewitness accounts, only to be exonerated later by more objective DNA evidence.12

In contrast, documentary evidence is often treated under special rules that can make it conclusive. For instance, in Anglo-American law, oral evidence is generally inadmissible if it seeks to vary or contradict the terms of a written agreement, effectively granting the document a binding status. While legal systems employ mechanisms like cross-examination to test the reliability of witnesses, documents remain a more stable, verifiable source of proof.13