The mystery plant is a common weed prevalent throughout North America and Europe. (Maybe other continents too?)
When you can identify it, please provide both the common and scientific names in a comment below. Also, there are two very common species of this plant. For “bonus points,” provide both of the scientific names. If you have any personal stories to share about this plant, feel free to include that in a comment.
ANSWER (subsequently added to this post to facilitate the “search” function for these images): English plantain (Plantago lanceolata)
Also, read the blog post and watch the plant portrait video for English plantain (Plantago lanceolata).