Shocked figuratively, but not literally. “Thrown for a loop” means surprised generally in a bad way. Imagine that you were the chief designer of a fast motorcycle, and your design is progressing OK. But then your boss said he wanted the wheels to be 10 cm in diameter. Such a directive would throw you for a loop. You wonder “What to do now?”
Related broadly to the overall discussion; one pet peeve is schematic diagrams with relatively few parts but drawn on large format, such as D size 22 x 34 inches. The problem is that the symbols are drawn small and the wires are drawn long. Zoom out to see the whole schematic and the symbols are too small to read. Zoom in to read some symbols and you cannot see the big picture. But the schematic could have easily been drawn with normal wire lengths on a smaller format so that it could be readable on a monitor or normal piece of paper. I do not know if there are any standards governing this sort of thing.
The mental image I associate with the phrase involves a pedestrian encountering an especially slick spot of icy walkway. The “loop” is the trajectory of his ankles becoming elevated above his cranium - definitely a bad surprise!
In the days of hand-drafted drawings on paper or acetate I saw such drawings a time or two. They came about when large portions of a circuit or system were entirely removed as a result of a design change, or moved to another sheet of the drawing (because more space was needed to show added circuitry).
A corollary situation is the sheet with so many components on it, perhaps tucked into corners and odd white space, that you can’t mentally decompose the thing into its constituent parts. It may be an artifact of my chronologically gifted status, but I want to be able to look at a schematic and say, for example, "Here’s the power supply, and I see there’s some input conditioning . . . and this is the low-level signal processing section, driving an A/D converter . . . . and over there is the power output stage, with some very basic protection circuitry . . . ", etc.
As I recall, in the U.S. both ANSI and the Department of Defense (DOD) had standards governing the form and content of technical drawings but I never gave them more than a cursory glance and even that was decades ago. I don’t know if they addressed the situation you described or not; I suspect that any attempt to do so was rather vague and subject to multiple interpretations. At some point it becomes an artistic skill, and some people are better at communicating their design intent through a schematic diagram than others. Published standards can go only so far. In Junior High School I suffered through endless evaluations against the standards of a “stylebook” (“The Elements of Style”, by Strunk & White), and several incarnations later an employer imposed its own stylebook (“The Tongue and Quill”, allegedly by one “Herb Schwartz”). Despite these efforts I am NOT - and never expect to be - on par with Hemmingway or Shakespeare.
Now that is pain I have known. In the 1990’s, my employer’s “standard” drawing size was E, which barely fit on a standard mechanical drawing table, but not on a desk with a lamp, name plate, and pencil container. This was also back in the days when an 18" monitor was a CRT and pretty expensive, so even looking at that stuff electronically was hard. We had a big HP roll printer for the E-size, but a few of us tried to keep schematics to B and C size for exactly the reasons you state, and because we could already print B size much quicker on the tabloid size laser printer. These days, I try to limit to a B-size sheet, opting for flat or hierarchical multi-sheet drawings when needed. At B-size, my 24" monitor is more than good enough to read the schematic all at once if needed, even with the sub-standard size (0.050" rather than standard specification for 0.12") designator and pin label text now commonly in use.
In my Marconi days 40 years ago, drawings were normally on A0 and the symbol sizes were determined by the plastic stencils that we used with the Rotring pens
Sorry, I mis-typed, I had tried the IEC webstore, and they would only sell a subscription but not a “snapshot” PDF or hardcopy. Again, for stuff that must be maintained and refreshed for more than a few years, that is folly. Any useful schematic that is more than a few years old should reference a standard or provide a key to symbols used. As is extremely clear from web searching, two different entities may understand the same symbol differently. This was made very clear to me when I recently found a web-only source that thought that the IEEE symbol for a capacitor with one straight and one arc line (but without a ‘+’ or ‘-’ symbol) represented a polarized capacitor.
I vaguely recall that this was not uncommon in the 1960’s. When you saw a ‘+’ or ‘-’ polarity symbol it was definitely a polarized (electrolytic) capacitor. If you saw the two parallel lines without a polarity symbol, it was probably a non-polarized (film, paper, or ceramic) capacitor, though you might quickly scan the whole drawing to determine which drafting standards were being used. A curved-line capacitor WITHOUT a polarity symbol often forced you to do more investigation, especially if the value was between 0.1uF and 10uF or so.
Actually in the ANSI/IEEE specification the one straight and one curved line symbol has been STANDARD since about 1962, and if ANSI Y32.2 or IEEE 315 was referenced on the schematic, that standard declared that without the polarity indicator (’+’) the part was non-polarized. A home-study NRI Radio and TV Repair course I finished in Jr. High explained that the curved symbol originally would indicate where the outer layer of the capacitor was, from the days of paper/foil wrapped capacitors with axial leads (one end had a bar marking showing outer layer).