Fossil and git have subtly different affordances while making a changes to a codebase.
fossil commit takes all changed files in the directory and commits those changes. This means that all files that have been edited in the project are committed at the same time, so a developer has to make sure that during a session, the changes made in the project have to be related to the current change/fix.
git add, aka. git stage adds a modified file to the index so that it will be included in the next commit. This means that you can modify multiple files and then selectively choose which files to commit. So a developer using git can work on multiple different changes in the same session and then selectively choose which to commit as a group.
Overall this difference in affordance means that a fossil user has to stay focused, but when using git a user can work on multiple different fixes concurrently.