There is always a gap between theory and practice. Many books give you no clue as to the size and location of the gap -- even books in exploration geophysics. This gap is nothing to be embarrassed about. It represents the current life of the subject -- the current life of any science. It is a moving target, and its size is a matter of opinion. So it is risky for me to tell you what works, what doesn't, what is important, and what isn't. Opinions go beyond facts. Your knowledge won't be complete if you don't know some opinions as well as the facts. You will be getting opinions as well as facts when I explain the discrepancies between theory and industrial practice, and when I explain what should work but doesn't seem to.