The book Thinking, Fast and Slow by Daniel Kahneman describes our brain as having two thinking systems, a fast one and a slow one. The fast system is automatic and multitasking, while the slow system is methodical and single-focussed. When you are doing something complex, you are usually concentrating your slow system on the main problem, while the fast system can be doing several related (and even unrelated tasks).

This is the main reason I try to memorize and practice several keyboard shortcuts for the programs I use every day. I am trying to get as much of the mechanics of the code editing into my automatic, fast thinking system.

There is a common belief that mousing is faster than keyboard shortcuts, which probably originated with this AskTog article:

We’ve done a cool $50 million of R & D on the Apple Human Interface. We discovered, among other things, two pertinent facts:

• Test subjects consistently report that keyboarding is faster than mousing.
• The stopwatch consistently proves mousing is faster than keyboarding.

This is probably true for the general case and for when the user is learning a new UI. But, the study, Comparison of Mouse and Keyboard Efficiency, suggests that:

[…] for heavily-used interfaces, keyboard shortcuts can be as efficient as toolbars and have the advantage of providing fast access to all commands.

For me, the key is that shortcuts have to be able to be deployed with no conscious thought.

Programming often requires you to keep several interrelated thoughts in your head until you get the code written and working. For example, even for simple web UI blocks, you have to think of the semantic structure of the tags, the layout, and the style. To write that code, you will have to possibly jump through a few files and parts of those files. So, to keep from adding more cognitive overhead, you want to make the manipulation of the editor as automatic as possible.

This is something I think that can never be accomplished with the mouse, but is possible for a small set of shortcuts. That set should be the most common actions that happen while you are actively programming. The goal is to keep your slow system and short term memory focussed on the programming task at hand.

For me, that is:

1. Cut, Copy, Paste, Undo, Redo
2. In-file navigation with arrows and modifiers (including using Shift for selection)
3. Find and multi-file Find
4. Show the current file in the project navigator
5. Open another file, tab cycling
6. Jump to the definition of the identifier under the cursor
7. Comment (or uncomment) the current selection

I do these commands all of the time. I often need to string a series of these commands together. Doing the equivalent without the commands risks engaging your slow thinking system and breaking you out of flow.