A little bit every day and you'll be there in no time.

EDIT: I should say, I took some time to go through every part of the diagram and it's been very helpful for forming a better mental model of Vim. It will look scary to the beginner, but for the moderate to advanced vimmer, this is a very useful learning tool provided you take some time to understand.

The thing about diagrams is that they often encode as much information as you might find in an essay, yet since the information is presented all at once, we have the expectation that we should be able to understand it immediately. It should take 10-20 minutes to understand this diagram.

Don't let this scare you. Learn 10 basic Vim principles and they will serve you 95% of the time. All this extra stuff can be learned incrementally on a case-by-case basis.

The great thing about vim is you do not need to know very much to be productive, but every day you learn something new that will make you more productive.

While this is a great reference writing a vim plugin or looking up the behaviour of a specific command, I don't really see it as a learning tool.

Modern shooters have become just as complex, with the various options available to you. If you can do those, you can use vim.

If you're still on the edge about Vim, there have been a few good articles on how to begin learning it. What worked for me personally was learning the very basics, how to enter insert mode, how to save and quit, and starting to use Vim as a regular mode-less editor while slowly learning about various useful things you can do in normal mode ("hey, I can delete a word or a line with two key presses"). That way you can begin to extract use out of it immediately while growing increasingly efficient with other modes.

If you're on a Mac, MacVim gives you native OS X shortcuts for things like Copy/Paste, and maps selecting text with the mouse to visual mode which, combined with using insert mode, gives you the same functionality as a regular mode less editor would.