Here is why experiential and usability testing are important: after over 30 years, it's still hard as fuck to use Microsoft Word to create a simple, unadorned, #10 envelope with a recipient and a return address. Designers should be forced to watch films of people trying this.
Here are some of the aspects of the problem. 1) You'd THINK that "envelope" would be one of the options immediately available from "File/New Document". Nope. A "World's Best" award certificate is offered, but not a damned envelope. Which template do YOU need more often?
2) Try searching online for "plain envelope". Reply: "We couldn't find any Word templates that matched what you were looking for." OK. "#10 envelope". That yields four results, of varying fanciness, but nothing straightforward and plain. Pick "Red" as the cleanest one.
3) Strip out the little bits of extra dross, enter the return address and the recipient's address. OK, not the font I want, but not too bad. Let's print that. Ctrl-P, and I shit you not, this is what I see. That's right: the return address is cut off BY DEFAULT. 
4) Change the margins so that the return address will be printed, but now it's in the wrong place for a return address and it looks stupid. Plus, what's that line doing there?
5) Go back to tweak it and I find the whole thing is rendered as a table. Weird. Hey... wait a second... there's that menu item that says "Mailings". Duh. And there it is, on the bottom left of the ribbon, "Envelopes"! And amazingly, it puts the return address in the right place!
6) Except... it puts the return address where the recipient's address should go, too. Dismiss the dialog, go back, select the recipient's address and paste it in. All right; not bad. Print! And... being old, I missed the tiny type: "Before printing, insert envelopes..."
7) "...into the following printer tray: Auto Select". So, without pausing, a page gets printed instead of an envelope. Also another bug: there are two feed trays on the printer, so "Auto Select" doesn't help. It should say "...into the following printer tray: the other one".
8) Word and Windows actually know a fair bit about my printer; they claim to know the proper orientation for the envelope. They don't, though; that's wrong. They also seem to have forgotten about the special document feeder at the back. That's the most convenient feeder.
9) Now it's the printer's turn. Word says the printer's in an error state. It psychotically comes to believe that there's a paper jam at the back of the printer. There isn't one. Try to shut it down, but it won't; "Busy; try later" and won't shut down until the paper jam clears.
10) This is a puzzler. Can't reboot the printer; having looked, I KNOW there isn't a paper jam. The printer insists there is one, front and back. Remove both feed trays. Fecklessly rattle some dangling equipment inside, as instructed. Now there's jam in the front. Progress.
11) Open some covers, examine some innards, rattle more stuff around. Printer sulkily says "please wait" for 15 seconds, and then admits that there's no paper jam. Good. Back to Word to reprint the envelope and... the Envelope dialog is gone, and the recipient address with it.
12) Based on past experience, I want to make sure that the return address is positioned properly on the page. There's a Preview icon there, but it looks like a default graphic, not an actual preview. If I click on the icon, I'll get a real preview.
13) So, I duly click on that icon in the field that says "Preview" This is the preview that I get.
14) Well... nothing to do but to try it and see what comes out. Based on the visual back there in tweet 12 of this series, I place the envelope in the printer's back manual feed slot *ahead of time* and press Print. The envelope emerges with the printing all skewed.
15) Jeez. OK, I take the paper out of tray number one, putting the envelopes in in the prescribed orientation. The envelope comes out printed on the back. (Only fooling! I actually skipped that step, anticipating that it would be wrong, so I set it up to come out right.)
16) Total investment of actual time: probably 30 minutes, not counting the time to compose this thread. For the fans of the old Get Smart, me trying to print envelopes is like Max and the Chief using the Cone of Silence. I don't know why I haven't learned.
