What happened Shares of Tesla (NASDAQ: TSLA) tumbled again on Friday. As of 12:27 p.m. EDT, the stock is down more than 1%, trading at about $400, but it declined to as low as $372.05 at one point during the trading day. The stock's pullback extends a downtrend for Tesla so far in September as many growth stocks have been falling sharply following a huge run-up in their share prices since April. Image source: Tesla. So what Tesla stock is down more than 15% in September. It's not surprising to see Tesla investors taking their profits, as the stock rose 500% between the beginning of the year and the end of August. Tesla's rapid gains in August, in particular, were arguably becoming irrational, as the primary news seeming to drive the stock higher was a stock split -- a structural change to shares that, in theory, does nothing to make them more valuable. Tesla's stock has also likely been declining because of a broader market sell-off in recent trading days that has been largely driven by profit-taking in growth stocks. Many growth stocks have significantly outperformed the market this year and it's reasonable to see them taking a breather after their impressive gains. Now what Investors should expect more significant volatility in Tesla shares in the coming days, weeks, and even months. Given its pricey valuation, which prices in years of rapid business growth, changes in investor sentiment about the company's long-term potential can have huge impacts on the company's share price. Find out why Tesla is one of the 10 best stocks to buy now Motley Fool co-founders Tom and David Gardner have spent more than a decade beating the market. After all, the newsletter they have run for over a decade, Motley Fool Stock Advisor, has tripled the market.* Tom and David just revealed their ten top stock picks for investors to buy right now. Tesla is on the list -- but there are nine others you may be overlooking. Click here to get access to the full list! *Stock Advisor returns as of August 1, 2020 Daniel Sparks has no position in any of the stocks mentioned. The Motley Fool owns shares of and recommends Tesla. The Motley Fool has a disclosure policy.Source