> why are you pressing the pause key to do something other than pause something?

because I do not use pause key for any purpose and single-key action are super-comfortable. For instance in my setup I open my mail dashboard (notmuch-emacs) with it's saved searches that I can open with a mouse click or a single key action again), tags etc simply hitting F6, shift+F6 open a mail compose buffer (window), F10 open firefox with a work profile, shift+F10 firefox with a personal profile, F7 open agenda, shift+F7 open agenda's main file etc.

It's far simpler, efficient and comfortable than click on some launchers that are always less than you need. Only I feel the pain that actual keyboards offer far less keys than in the past...

> How many letters do you write a day for it to need to be optimized into single key shortcuts?

I write them rarely, but I have no shortcut for letter but for ANY documents, the pause keys simply popup a menu that present me some personal choices (letter, reports, slides, projects of various kind and languages etc), I choose one from the list and find it pre-made as much as possible. Only for letter I use normally double-window envelope that to work properly demand a certain position, certain address format, certain fonts etc. If I made them by hand and rarely I certainly make mistake, have template them once I can write straight away painless. It does not cost me substantially anything, only around half an hour once in my life and pay back at any letter I write. Same for slides. It took few hours to made few personal template and after I can only write down contents. Same for thesis, reports, ...

Basically a step at a time I crate my digital environment thanks to Emacs and now I have anything at my fingertips at an unprecedented level and essentially at no cost since I add stuff when I have time, calm, without pressure nor frustration and I found it back when I need and perhaps I'm on hurry.

For instance I have regular invoices by mail (telephone, electricity, water supply bills) in the past I spend few time regularly to read them (I normally have them auto-paid by the bank) and archive by hand. Now thanks to notmuch hooks I have simple scripts that when a known bill arrive archive it accordingly and add a small note to my startup dashboard. So now when I have time I read the bill with a simple enter in the dashboard, when I quit the entry goes away from the dashboard and anything is done. If the correspondent payment does not show up in ledger (personal accounting) after some time (actually I'm not developed anything that guess when to expect the payment from an invoice) an alert popup in my dashboard and when I open it I found in a click/enter the "unmatched" invoice...

I have similar automation, all made in free time when I'm willing to build, for mail autorefiling (IMAPFilter), with Alt+F6 (my "official mail key") I go straight to unread mails or get a "no unread mail" message in the minibuffer echo area and mail are automatically refiled as much as possible in their proper dir. After a certain amount of time and depending of mail directory IMAPFilter automatically delete the message helping me keep my mails clean and easy to search. When an unread message need to be left around for some reason I may add a proper tag to snooze or categorize it in some temporary way, few tags can be added by single keypress on the message, for instance 'l' add "live" tags that automatically show up in general dashboard, and mail dashboard, O add "order" tags for online shopping done but waiting to receive the package, T add todo tag etc.

It's more complicate to explain it than build thanks to Emacs and again I'v build in baby step and more other will come, when I feel the need for it or I'm curious or simply I have free time and willingness to automate some things.

That's in synthesis an ecosystem tailored to my needs, thanks to flexible and easy to customize software, that keep me evolving everyday. All other environment I know are like a wrench: can be useful for doing few things but can't really be customized nor evolved.