Module setting instance variable and then checking for that variable in a containing class

Module Instance Variable

[1] pry(main)> module Helper
[1] pry(main)*   def set_stuff
[1] pry(main)*     @stuff = 'something'
[1] pry(main)*   end  
[1] pry(main)* end  
=> nil
[2] pry(main)> class Controller
[2] pry(main)*   include Helper
[2] pry(main)*   def index
[2] pry(main)*     set_stuff
[2] pry(main)*   end  
[2] pry(main)* end  
=> nil
[3] pry(main)> c = Controller.new
=> #<Controller:0x1043bb488>
[4] pry(main)> c.index
=> "something"
[5] pry(main)> c.instance_variables
=> ["@stuff"]
[6] pry(main)> c.protected_instance_variables
NoMethodError: undefined method `protected_instance_variables' for #<Controller:0x1043bb488 @stuff="something">
from (pry):15:in `__pry__'
[7] pry(main)> 
[7] pry(main)> module Helper
[7] pry(main)*   def set_stuff
[7] pry(main)*     @stuff
[7] pry(main)*   end  
[7] pry(main)* end  
=> nil
[8] pry(main)> c2 = Controller.new
=> #<Controller:0x10457d9b0>
[9] pry(main)> c2.index
=> nil
[10] pry(main)> c2.instance_variables
=> []
[11] pry(main)>