Installing gems is hard

gistfile1.txt

mark:~ $ which ruby
/usr/bin/ruby
mark:~ $ sudo gem install ronn
Building native extensions.  This could take a while...
Building native extensions.  This could take a while...
Successfully installed hpricot-0.8.4
Successfully installed rdiscount-1.6.8
Successfully installed mustache-0.99.4
Successfully installed ronn-0.7.3
4 gems installed
Installing ri documentation for hpricot-0.8.4...
Installing ri documentation for rdiscount-1.6.8...
Installing ri documentation for mustache-0.99.4...
Installing ri documentation for ronn-0.7.3...
Installing RDoc documentation for hpricot-0.8.4...
Installing RDoc documentation for rdiscount-1.6.8...
Installing RDoc documentation for mustache-0.99.4...
Installing RDoc documentation for ronn-0.7.3...
mark:~ $ which ronn
/usr/bin/ronn
mark:~ $ man ronn
No manual entry for ronn
mark:~ $ 
mark:~ $ rvm 1.9.2
mark:~ $ which ruby
/Users/mark/.rvm/rubies/ruby-1.9.2-p290/bin/ruby
mark:~ $ ronn --help
/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems.rb:777:in `report_activate_error': Could not find RubyGem ronn (>= 0) (Gem::LoadError)
	from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems.rb:211:in `activate'
	from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems.rb:1056:in `gem'
	from /usr/bin/ronn:18
mark:~ $ 
mark:~ $ rvm system
mark:~ $ ronn --help
Usage: ronn <options> <file>...
       ronn -m|--man <file>
       ronn -S|--server <file> ...
       ronn --pipe [<file>...]
Convert ronn source <file>s to roff or HTML manpage. In the first synopsis form,
build HTML and roff output files based on the input file names.

Mode options alter the default behavior of generating files:
      --pipe                write to standard output instead of generating files
  -m, --man                 show manual like with man(1)
  -S, --server              serve <file>s at http://localhost:1207/

Format options control which files / formats are generated:
  -r, --roff                generate roff output
  -5, --html                generate entire HTML page with layout
  -f, --fragment            generate HTML fragment
      --markdown            generate post-processed markdown output

Document attributes:
      --date=<date>          published date in YYYY-MM-DD format (bottom-center)
      --manual=<name>        name of the manual (top-center)
      --organization=<name>  publishing group or individual (bottom-left)

Misc options:
  -w, --warnings            show troff warnings on stderr
  -W                        disable previously enabled troff warnings
      --version             show ronn version and exit
      --help                show this help message

A <file> named example.1.ronn generates example.1.html (HTML manpage)
and example.1 (roff manpage) by default.