But you've still gotta do your homework.
Is a stock a quality one that's down just because the market in general is down, or is the stock down because the company has some serious issues, or in a fading industry? If it's the former, yeah, good time to buy. If the latter, and the stock is down for a reason, then buying would be throwing money away.
A bit about how the stock markets work:
About 80% of all stocks are owned by institutional investors: pension funds, mutual funds, IRA's, 401k's, hedge funds. There are tens of thousands of people who work for these funds as stock analysts. For them, the beginning and end of their job is beating whatever stock index is the benchmark for their fund. If they can do that they make lots of money, if they don't they lose their job.
If your benchmark is, say, the S&P 500, the easiest way to keep your job and make lots of money is to look at the 500 companies in the S&P 500, try to identify ten or so that you think will underperform the index overall, and buy the other 490 or so. On average the S&P 500 has returned slightly over 10% per year since 1957, so you're looking for a handful of companies that you expect the price a year from now to be less than 10% above the current price.
At the same time, tens of thousands of other analysts are doing the same thing. And together, you control 80% of the market. If a bunch of you think a stock will underperform the market and you all sell it, its price will drop. And it will drop until the current price is low enough that it becomes as good an investment as any other stock in the market.
Similarly, if a bunch of analysts think a company will out-perform the market, they will bid the price up until it's no better an investment than any other stock.
In general, at any given moment, all stocks should be expected to be equally good investments. The exception would be if you have information not available to the rest of the market. But for an ordinary investor it's unreasonable to think that you can look at a stock and see if it's a good investment. The market is already doing that work for you.
If you'd like to learn more, I recommend a classic text, "A Random Walk Down Wall Street" by Burton Malkiel. It's in its 13th edition and has been continuously in print for over 50 years.