System in OS X 10.11.4 El Capitan
$ cd $HOME
$ ls .
> Dropbox
> BTsync
Code which creates unsuccessful symlink
ln -s BTsync/ Dropbox/
Code which creates working symlink
ln -s /Users/masi/BTSync/ /Users/masi/Dropbox/
Evidence in size difference with files
$ cd $HOME
$ ln -s $HOME/BTsync/wfdb.zip $HOME/Dropbox/
$ ln -s BTsync/wfdb.zip Dropbox/wasi.zip
$ ls -la $HOME/Dropbox/
lrwxr-xr-x 1 masi staff 41 May 17 22:45 wfdb.zip -> BTsync/wfdb.zip
lrwxr-xr-x 1 masi staff 46 May 17 22:45 wasi.zip -> /Users/masi/Dropbox/wfdb.zip
Evidence with directories
$ ln -s /Users/masi/BTsync/cam\ local/ /Users/masi/Dropbox/
$ ln -s BTsync/cam\ local/ Dropbox/camLocal2
$ ls -la $HOME/Dropbox
lrwxr-xr-x 1 masi staff 37 May 17 22:52 camlocal -> /Users/masi/BTsync/cam local/
lrwxr-xr-x 1 masi staff 25 May 17 22:53 camLocal2 -> BTsync/cam local/
and visually same in Finder
which shows that the two commands are not the same in El Capitan. Using absolute PATH only works.
Evidence with Relative PATH
$ cd $HOME
$ ln -s ./BitTorrentSync/cam\ local/ ./Dropbox/camlocal3
$ ls -la Dropbox/
lrwxr-xr-x 1 masi staff 27 May 17 22:58 camlocal3 -> ./BTsync/cam local/
and a new screenshot
Why OSX Symlink cannot Relative PATHs?