"Self, I'll just sell these shares, take the loss on my tax return, and then immediately buy those shares back. I'll be able to keep the stock I really like and take a tax loss all at the same time. Sweet."
Don't do it unless you know the rules. You might run afoul of the wash sale rules. "What?" you may say. We're not talking about beating our shirts against a rock here, we're selling stock!
And, while that very well may be true, Uncle Sammy doesn't see the humor in the fact that you're retaining your economic position in your stock while buying yourself a tax deduction with no risk to you in the future. Therefore, to close this glaring loophole, the Feds long ago named this transaction a "wash sale" and deemed that any loss on a wash sale could not be currently recognized.
Wash Sales Under the wash sale rules, if you sell stock for a loss and buy it back within the 30-day period before or after the loss-sale date, the loss cannot be immediately claimed for tax purposes.
This rule is designed to prevent you from selling stock to claim the loss and then buying it back within a short period of time to retain ownership. Note that the rule applies to a 30-day period before or after the sale date, to prevent "buying the stock back" before it's even sold.
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