title: Why does on_message() stop commands from working?
body: <p>Basically, everything <em>appears</em> to work fine and start up, but for some reason I can't call any of the commands. I've been looking around for easily an hour now and looking at examples/watching videos and I can't for the life of me figure out what is wrong. Code below:</p>
  
  <pre><code>import discord
  import asyncio
  from discord.ext import commands
  
  bot = commands.Bot(command_prefix = '-')
  @bot.event
  async def on_ready():
      print('Logged in as')
      print(bot.user.name)
      print(bot.user.id)
      print('------')
  
  @bot.event
  async def on_message(message):
      if message.content.startswith('-debug'):
          await message.channel.send('d')
  
  @bot.command(pass_context=True)
  async def ping(ctx):
      await ctx.channel.send('Pong!')
  
  @bot.command(pass_context=True)
  async def add(ctx, *, arg):
      await ctx.send(arg)
  </code></pre>
  
  <p>The debug output I have in on_message actually does work and responds, and the whole bot runs wihout any exceptions, but it just won't call the commands.</p>