Tesla's (TSLA 6.26%) stock has come down considerably since the year began. Shares are down roughly 30% in value so far this year, with the stock's price-to-sales ratio falling from over 15 to just 9.2.On paper, Tesla's valuation looks compelling. But there's one factor that investors must understand before jumping in.Tesla's stock isn't as cheap as it looksThere's no doubt that Tesla's stock is much cheaper than it was just four months ago. But when you zoom out further, it becomes obvious that most of thi ...