In one of my early studies, I examined the factors affecting the optimal size of a construction crew. My list of factors was very elaborate, and included worker's experience, foreman's training, complexity of work, and many others.
I collected data via field interviews and on-site productivity measurements both in Texas and Israel. However, only after I completed
collecting my data did I learn that I failed to include one simple but sometimes very crucial factor. It turned out that for some trades in Israel, the deciding factor for the size of the construction crew was no more nor less than the size of the pickup truck carrying the workers from their remote villages to the site. Literature surveys and field pre-testing of the interview guide were insufficient. Deep acquaintance with the phenomena under study is the key.
Only when the researcher acquires a rich and intimate knowledge of the subject, or when the practitioner serves as an active partner in helping the researcher formulate the right questions and design the right research tools, will any of us learn something meaningful.