The Accountability of Witnesses

It's not news that human beings can't remember things with 100% accuracy. After all, most of us can barely remember what we ate for dinner the night before. But in a court of law, how exactly do we address this issue? When there are instances where a witness's testimony is easily seen as inconsistent with others, how does our justice system hold them accountable for this fact? How do we separate what was actually seen and what is merely speculations after interacting with others? And for those whose testimony are proven to be inaccurate in some aspects, do we through out their entire testimony or do we disregard all the discrepancies? 

If there is a recording of an initial interview that contradicts what was said in court, what do the jurors prioritize? Personally, I would prioritize the initial interview when the witness have not had sufficient time to interact with others and modify their story, consciously or not. Unfortunately, if the witness have had time to interact with others, we arrive that the same crossroad of what we should believe and how we can identify the most accurate statement.