"[this proof/investigation/question] ... is left as an exercise for the reader." Was it just us engineers and mathematicians and statisticians who had to endure this textbook taunt?

How many of us readers actually did the exercise, and worked out the issue? How many of us chose to be mental couch potatoes instead, sitting in front of the Idiot Book and accepting whatever it had to spew at us? I have no problems admitting I am a member of the latter, with my butt print firmly imprinted in the comfy chair that was apathy: apathetic of the course, its foundations, its implications. Academia had so far-removed the topic from my reality and from my realm of concern that it didn't really matter to me how many poles were in the right-hand plane, or when to apply Euler's formula. I just didn't (and still don't) care.

And while I will simply accept that certain formulae work and hold true, those are not the topics that I will remember far into a useful future. Instead, I need a strong tie to reality and to real-world applications, before I will accept a new concept. Concepts: broad understandings of certain phenomena, generalizations that explain many cases at once, but allow the individual to judge for themselves when anomalies and exceptions should apply. Consider it a blanket statement (know it's got its holes) packed into a tiny nugget of information. Maybe the ultimate in efficient learning, and the least strain on the brain.

That's just how I prefer to learn.