Git出错 Fatal:multiple Stage Entriesfor Merged File

Question

I have encountered this situation several times

GIT error:

fatal:multiple stage entries for merged file

You can easily find the corresponding solution by searching online. The solution is as follows:

rm .git/index
git add -A
git commit -m 'fix git fatal error'

But why does this error occur and how to avoid it. I hope friends who know the reason can help me answer my doubts.