bool productPricingUpdatedAfterDeliveryFailedButEmailSent = false;
This kind of thing can be broken into multiple Booelan variables:
bool pricingUpdated;
bool deliverySucceeded;
bool emailSent;
if (pricingUpdated && !deliverySucceeded && emailSent) ...Single letter variable names are okay for loop iteration variables, or e.g. x and y when dealing with 2D coordinates (i.e. if within the context a single letter name has useful meaning - I suspect physicists and the like find themselves in that situation often).
But trying to give variables short names (which is a good thing) should not be an excuse to give them obscure names.
As an extreme example, think of Perl, which has a "default variable", that has basically no name at all ($_). When used properly, one can, I guess, write marvelously succinct code, but I try to avoid it and use explicit names.
The older I get, the more I tend to agree with Aristotle's general approach to ethics: Avoid extremes, seek a middle ground/moderation. I am not sure if it is a good ethical principle, but in many cases where ethics don't matter, it is a good guideline.
So for Identifiers: Be short, but clear. When in doubt, choose clarity over brevity, but keep in mind that what might be clear to you could be highly obscure to somebody else. If at that point I was still in doubt, I would pick a name based on how the variable is used: The more rarely it used, and the more significant it is to the program, the more reasonable it becomes to use a verbose name, especially when it is a global variable. For locals, one can always use a short name and a comment to explain what role it plays.