Beginner Question:Why it always make sure that the postgres better than common csv file storage in disaster recovery?

[Wen Yi]

I am a student who are interesting in database kernel.When I am 
reviewing my database course,a question make me confused.

In file system,if a error happen when I insert some data into data 
saving system,the whole data exists will be broken and can't recovery 
anymore.

But when I check the code in postgres,I found the postgres also use the 
write function(That! is a UNIX file system api)

My question is:

Since it's all built on top of the file system,why it always make sure 
that the postgres better than common csv file storage in disaster 
recovery?

Thanks in advance!