The truth is that there are many situations and sentences which allow for either the past perfect tense or the past simple tense, with very little change to the sentence. The key difference between the past perfect and past simple tenses is the explicit order of two (or more) events in the past. There are of course many nuances in usage that make this a fairly complex topic, which I can only partly cover here. First, here is a brief overview of some of the relevant usages and rules of past simple and past perfect:
The third point is where the past simple tense overlaps with the past perfect tense, and is what I will be focusing on.
Simple tenses are often represented as a single dot on a timeline, such as the one below. In the case of past simple, this represents that the event is completed entirely in the past. If past simple is used to list multiple events, then we represent it with multiple unconnected dots in the past, arranged in chronological order.
The two events have a specified order, so chronological order and explicit times are uncessary.
Perfect tenses are often represented by two dots with a connecting "bridge" on the timeline. This represents both the order (past perfect clause = left dot; past simple clause = right dot) and linking of the two events.
e.g. I had already eaten breakfast when my brother arrived.
Note: I find that timelines such as this often help my students understand tense usage better. This particular timeline is one I use often and is from this site.
The past perfect is not necessary if we are not 'going back' to the earlier past, and simply moving from one event to another.
This is correct. Past simple can be used to list multiple events in the past, but they should always be in order of occurrence, from longest ago to most recent (or have some other way of explicitly stating the order of events).
Yesterday I went to work, and then did some shopping.
If we use the past perfect tense instead, then we have more flexibility in the sentence structure while still being grammatically correct.
I had gone to work yesterday before I did some shopping.
or
I did some shopping yesterday after I had gone to work.
You can see that when using the past perfect tense we can list events in whichever order we prefer, rather than being restricted to chronological order.
If the sequence is clear, the past perfect is not needed.
Again, this is correct. However, there are nuances here. For the sequence to be "clear" you must either list events in chronological order as I mentioned before, or explicitly state the order or time in the sentence. This is often ignored by native speakers because the order of events can usually be inferred from the sentence without it being explicitly stated. In fact your example sentence shows this phenomena. I will again denote longest ago and most recent.
We showed the result of the survey we did.
We can in this case correctly infer that the survey was completed before the results were shown, it is simple logic. However, if you wish to be more clear (and grammatically correct) then it is better to write it in the past perfect tense.
We showed the result of the survey we had done.
I recommend my students to always use explicit ordering of events for the sake of clarity, so that the reader/listener does not need to use logic to deduce the order. Most prefer to do this by using the past perfect tense, or chronological order of events in the past simple tense.
The past perfect is optional [i.e. may be replaced by past simple] only when talking about an action at a specific time.
This "rule" is a combination of the usage rules for past simple and past perfect. As I mentioned before, one of the rules of past simple is that it must include a time, which can be either implied or specified. However, when the past simple is used to replace the past perfect, more information (i.e. a specific time) is needed to provide the same information to the reader/listener that the past perfect tense would have given.
Best Answer
This "authority" is in error; the past perfect is not necessarily required here, although there are circumstances in which it would be preferred in formal discourse, and the simple past is not incorrect, although there are circumstances in which its use would be deprecated in formal discourse.
This is in the first instance a matter of context— specifically, what you are trying to express and what time you are talking about, what grammarians call Reference Time.
Perfect constructions do not express events prior to Reference Time; they express a state grounded in prior events which obtains at Reference Time. So if you are talking about a time in the past when your subject's previous unfamiliarity with bears was of immediate relevance, the past perfect will be appropriate:
But if your Reference Time, the time you are speaking about, lies before the time at which she moved to Alaska, a past perfect will not be appropriate:
In less cut-and-dried circumstances, usage varies: formal usage and British colloquial usage tends to employ the past perfect more often than US colloqual usage. If you have an appetite for technical grammar, I modestly recommend our Canonical Post on Perfect Constructions, particularly sections 3.2 and 4. If not, the best 'rule of thumb' respecting use of the past perfect is FumbleFingers‘ Perfect Truism: