Buying back shares is not unsustainable in and of itself. Buying back shares to artificially inflate your stock price is. The unsustainable part is giving inve

Buying back shares is not unsustainable in and of itself. Buying back shares to artificially inflate your stock price is. The unsustainable part is giving investors the impression that, while the Dow plunges 500 points, your stock remains stable. Then when your buybacks stop and your shares plummet with the rest of the market, it gives the impression that something suddenly happened and your company is in a dire situation. Either you keep buying shares to inflate the value (which gets expensive) or you stop and accept that your shares will go down (which looks worse now that your stock price has not declined with the rest of the market). Either way, if you're using buybacks to keep your stock price up in a market that's down, you're going to get burned eventually.