In logic, using a tree, it is easier to trace back from some node (leaf) to a basis node. And, in trees, the basis can move around. The inverse is much harder; that is, trying to expand any tree forward. Same thing goes for lots of problems, in general. It is harder to find solutions than it is to check them (core of the complexity issues related to CompSci).
Do not believe me about this? Take armchair quarterbacks, as an example (or anyone being critical). In another view, look at the Mayflower group's Silver series; this work has been on-going for a century and is still being updated. Mind you, that is look forward only five generations. We have talked about such an effort for the descendants of Thomas and Margaret (search on 'generations') and have proposed two to three generations. And, one thought was to try to get up to 1900. If you look at Dr. Frank's books, his 1907 issue was mostly of Samuel with a little George thrown in; 1933 was of George's contributions.
Now, compare the coming forward with the ease (relatively) with the look back needed to prove some lineage -- I have done dozens of these and saw one estimate (same contextual framework) claiming 90% success when there is a good database, barring the conditions that we see leading to brick walls, whether these are real or of some attitudinal shortcoming.
Of late, we spent considerable time looking at heritage using a known database which supports applications. In one case, the merging of three lines (snip, paste) resulted in a documented line from an applicant to an ancestor about eight generations back. Usually, these new nodes (where the snip/paste happened) need some additional work. Why? The originals might have used one of the parents whereas the new look goes with the other. So, lessons learned there.
Too, we used WikiTree to do Dr. Frank's lineage back. It is fairly complete (Gardner-11627). Where there are holes, we have things to stuff in once they are confirmed. As well, we have run across several descendants of Benjamin Brown Gardner and Lucy Foster Wilson. There were papers related to this that got mention in the NEHGR 2017.
In one case, we have corresponded with a great-grandson of Dr. Frank. A post on Dr. Frank last Veterans' Day showed stones of another great-grandson. These were descendants of both wives of Dr. Frank. Then, part of the WikiTree work that we have adopted was done by another descendant of BBG. Starting with Jeffry's node on Abel, son of Samuel and grandson of Thomas who was buried near him in Gardner's plot, one gets to BBG. There, one finds two sons, for now: the father of Dr. Frank (Stephen Wilson Gardner) and his brother (Walter B Gardner). Ann's great-grandfather, Joseph D. Gardner, was their brother (see image).
From this generation, we can build family records and match up across the tree. For instance, we saw a descendant of Benjamin Brown's brother last year when a photo of him was published in a FaceBook group dealing with old photos: Thomas Needham Gardner. Thomas was a great-uncle of Dr. Frank and Ann's grandfather.
We started a series looking at people of a particular name. In one case, we used Elizabeth. We expect that a consistent approach like this will allow us to document a whole lot of the tree. We want to hear about the work of others, too.
Remarks: Modified: 07/28/2020
07/28/2020 -- Have done several posts related to generations: 5th generation, 6th generation, 7th generation, 1900 back, American 100s, First five, and About generations.