I don't get it. Can anybody explain to me what is happening here?

method_test.rb

#! /usr/bin/env ruby

module Helper
  def help1
    @help1 ||= [ :success1 ]
  end
  def help1=(a)
    @help1 = a
  end
  def help2
    @help2 ||= [ :success2 ]
  end
end

module Tester
  def test
    @a = "Hi, I never changed the @a variable."
    if false
      puts "Hi, I'm doing this."
      help1 = [ :failure1 ] 
      @a = "This should never happen."
    end
    puts "help1 # => #{help1.inspect}"
    puts "@a    # => #{@a}"
    puts "help2 # => #{help2.inspect}"
  end
end

class Klass
  include Helper
  include Tester
  def initialize
  end
end

class Test
  def initialize
    @a = Klass.new
    @a.test
  end
end

Test.new if __FILE__ == $0

output.txt

$ ./method_test.rb 
help1 # => nil
@a    # => Hi, I never changed the @a variable.
help2 # => [:success2]

And yet, if one comments out line 20 of method_test.rb, then both help1 and help2 will contain :success. I don't get it.