Why won't iTunes copy my new mp3 to the iPod? I have a new mp3 in iTunes, and despite how many times I sync it with my iPod, the new song will not be copied. I tried to remove all songs from that artist, and add again, but the new song is still not on the iPod.

There is no message or indication of an error.

Any idea what's wrong here? (using a fourth-gen iPod touch and iTunes 10)
As @iampearce answered in the comments:


  If you're manually syncing, grab the file from in iTunes and drag it
  onto the iPod itself. This will force it to copy over, and you'll be
  able to see it happen in the progress bar.