github - git checkout -f problem

Question

Git novice questions
Scenario: I build git locally and then associate it to the github warehouse, and the server pulls content from github.
Problem: After pulling it on the server, I modified a file locally. After pushing it to github, github updated the content I changed, but an error occurred when pulling it on the server: error: Your local changes to 'yourfilename.html' would be overwritten by merge. Aborting.
After checking this error report online, it said that you can just pull it after git checkout -f. After I executed the git checkout -f command, I found that the permissions of this directory were lost. What happened?