I would appreciate you can refer to scholarly papers, chapters and articles shedding light on the historical development of the qualitative research paradigm.
When I started diving into the topic as a student, I found articles from Maura Dowling helpful. They sketch a rough oversight of the topic, while applying a critical perspective on the blurriness of application of the paradigm in a range of cases today. It might be a good entry point before going into detail.
When would one want to use observation or interviewing? When there are multiple causal factors that are difficult to specify in advance, an open ended inductive exploration is called for. If it is not a process where A causes B, but rather A and B are interacting, conducting fieldwork would be the best course. Fieldwork can explore how interpretations are rendered. If one takes a simple object like a tree, it could mean something quite different to a child, a painter, a logger, etc. The only way to understand what the tree means to these various people is to put yourself in their shoes.
I think the best two sources on Symbolic Interactionism are listed below:
Blumer, H. 1969. Symbolic interactionism: Perspective and method. Englewood Cliffs, NJ: Prentice-Hall.
Rock, P. 1979. The making of symbolic interactionism. Totowa, NJ: Rowman and Littlefield.
There are a number of game changing books . Here are some of them, listed by date.
Goffmann, E. (1959). The presentation of self in everyday life. New York, NY: Anchor.
Watzlawick, P., Beavin, J. H., & Jackson, D. D. A. (1967). Pragmatics of Human Communication: A study of international patterns, pathologies, and paradoxes. Norton.
Glaser, B. G, & Strauss, A. L. (1967). The discovery of grounded theory: Strategies for qualitative research. New York, NY: Aldine De Gruyter.
Geertz, C. (1975). The interpretation of cultures. New York, NY: Basic Books.
Recent, but excellent overview: Tracy, S. J. (2010). Qualitative quality: Eight “big-tent” criteria for excellent qualitative research. Qualitative inquiry, 16(10), 837-851.
The best historical overview of the "moments" of the qualitative paradigm is in Norman K. Denzin & Yvonna S. Lincoln's "Handbook of Qualitative Research" (several editions), published by Sage.
I have to say that I've always been amused by Denzin and Lincoln's "moments" -- prior to 1985 or so, multiple decades go by without a moment, but once our authors appear on the scene, moments start happening every 2 or 3 years. Sigh...