No matter how great a stock looks, diversification is better. Always spread your investments & spread your risk.
You know what happens to guys who put their whole savings into one investment? I'll tell you what happens to 'em. They end up humping crappy jobs on graveyard shifts,trying to figure out how they came up short. See, every investor has this picture in their head about getting rich quick and sitting back in luxury the rest of their life. And they let that vision blind them to reality, which is diversify or eventually perish!