You run a 'git status' and see that you've updated a heap of files. One of those files you don't want to commit (often a config). What's the easiest thing to do? Well, I have a few options.
Option 1. Use 'git assume-unchanged'. I have a blog post about that here: https://dev.to/nickraphael/git-assume-unchanged-for-when-you-want-git-to-ignore-an-edit-for-a-while-2lig
Option 2. Just undo you edit before doing the add. Basically using 'git checkout xxx/dontcheckmein.txt'
Option 3. Run a 'git add .' to add all the files. Then run 'git reset -- xxx/dontcheckmein.txt'. This will undo the add.
Then you can 'git commit' to your hearts content.