This might be one of the only places around where you hear people go "dangit!" when their stocks go up, or mutter under their breath in disbelief.

Quite often, we're shouting or muttering because we'd like to buy more of what we think is a good thing, and we like it as cheap as we can get it. (I'll take more cheap Microsoft (NASDAQ:MSFT), please.)

Other times, such as yesterday and today, we're muttering because Mr. Market is just plain kooky. Take the case of SanDisk (NASDAQ:SNDK). Thursday it jumped nearly 10%, and it's up another 4% Friday. Don't get me wrong: As someone who holds those shares, that's fine with me. But on the other hand, it's really pretty silly.

The jump follows an upgrade from a Citigroup (NYSE:C) analyst. The reports cite the big demand for flash memory that's likely to be coming down the pike, a demand that even us amateur Fools could see a few weeks back. With Apple (NASDAQ:AAPL) shelling out billions up front, it doesn't take a bow tie or an MBA to figure out the demand picture.

So, it's nice that more of us agree, but the goofy price jump also offers us a chance to point out just how fitful the markets are. Only a couple weeks back, the market sold off SanDisk in a big flurry just because some other analysts began laying it on thick, Cramer hit the panic button, and all were predicting more than a bit of doom in the face of a new flash memory partnership started by Intel (NASDAQ:INTC).

Now, I won't try to argue that this isn't a risk. But I think it's less of a problem than others predict, and the recent exit of Renesas from this market -- at a time when demand can't keep up with supply -- tells me that this is a space where the leaders will thrive and others won't survive.

That's why I'd also say that SanDisk is still an OK buy, even though it doesn't look cheap. To me, it's one of those special tech leaders that fits into the "I don't know what it's worth, and neither do the analysts" categories. It's enough that it's at the front of a market with huge and growing potential, something akin to Electronic Arts (NASDAQ:ERTS) or Activision (NASDAQ:ATVI) in games.

But if I think the stock is OK now, it was a much better deal a month ago. That might sound obvious, but the recent price action in SanDisk suggests not everyone sees it that way. Remember, nothing substantive has changed between then and now, except for what a few people have said about the company. People from a class of observers whom, we should note, are not always right about getting the particulars when it comes to the earnings crystal ball.

I believe anyone who holds SanDisk from here will see market-beating gains over the next few years. But had you gotten your shares at any one of several points in November, you'd already be sitting on a 20%-plus gain. Clearly, if you believed at all in SanDisk's future, the smarter time to buy was then, not yesterday or today.

In the end, the lesson is crystal clear. You can make money buying high and hoping for higher, but it's much easier to sell high if you buy low. When the frenetic markets give you the chance, take it.

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Seth Jayson has been known to buy high and sell low from time to time, too. At the time of publication, he had shares of Microsoft and SanDisk, as well as covered calls on the latter, but no position in any other firm mentioned. View his stock holdings and Fool profile here . Electronic Arts and Activision are Motley Fool Stock Advisor recommendations. Microsoft is an Inside Value pick. Fool rules are here .