If you sell it now, you will have succeeded in applying the "buy high, sell low" strategy of investing.

The real question is, why did you buy it, and what did you hope to get out of buying it?

If you bought it planning to hold it for a long time since, in the long term, stocks (of stable companies) go up, then you should probably stick to your plan of holding it. Assuming, of course, you think that US stocks will recover in the long term (good bet) and that you think AutoZone is a stable company that will be around for the long term. This also seems like a good bet since retail auto parts is not a market that sounds like it's going away (especially in a downturn, when people look for ways to save money), and AutoZone has a good grip on it.

If you bought it planning to turn around relatively quickly and sell it for a profit, then I have no advice to offer. I don't gamble very much and thus don't have much insight on gambling.

Two final thoughts:

(1) If you were buying for the long term, it seems like you might have also diversified more (although I don't know that you didn't -- maybe you have LOTS of money).

(2) Sometimes it's smart to get out while you still can, but don't let emotions -- specifically, fear -- push you into pulling out of something. AZO isn't the only stock that has fallen a whole lot.