I've been a professional C, Perl, PHP and Python developer.
I'm an ex-sysadmin from the late 20th century.
These days I do more Javascript and CSS and whatnot, and promote UX and accessibility.
Make using the mouse a thing that you notice, because you almost certainly don't notice it right now. Put something on your mouse like a post-it note. It'll feel a little uncomfortable to use, and each time you reach for it you'll notice.
Once you're aware (in more than a vague, goal-oriented way) of how much you're using it, think each time you use it, "did I need to use the mouse for this action?"
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Make using the mouse a thing that you notice, because you almost certainly don't notice it right now. Put something on your mouse like a post-it note. It'll feel a little uncomfortable to use, and each time you reach for it you'll notice.
Once you're aware (in more than a vague, goal-oriented way) of how much you're using it, think each time you use it, "did I need to use the mouse for this action?"