BA7ANCE is based on one of the most highly cited papers in psychology by Miller, G. A. (1956). "The magical number seven, plus or minus two: Some limits on our capacity for processing information". Psychological Review. 6.
The word "magic" in this case was used rhetorically, as it varies from person to person in terms of their cognitive ability and short term memory span. Later research concluded that the limits depend on "chunks" of information, and the span is around seven for digits, around six for letters, and around five for words.
The number seven is not an absolute but rather a useful heuristic that even telcos used when assigning phone numbers (less the area code, they are seven digits).
BA7ANCE is bolstr's Pocket Research philosophy backed by half a century of cognitive research reminding us that "chunks" longer than seven inevitably become significantly harder to remember and process simultaneously. Therefore, we do not design bags and accessories with more than seven pockets.