You would expect >> to be somehow analogous to <<, but it isn't really. It simply means to append the output to a file, rather than overwrite as > would. For example:

$ echo Hi > myfile
$ echo there. > myfile
$ cat myfile
there.

Oops! We lost the "Hi" portion! We meant this:

$ echo Hi > myfile
$ echo there. >> myfile
$ cat myfile
Hi
there.

Much better!