A. It really all depends on the makeup of the cigar and how you smoke it,; sometimes it's a combination of the two.

Many cigars tend to get bitter in the last third because tars tend to build up as the cigar is smoked. But a well-blended cigar that remains consistent in flavor into that final third (and lets assume you are really enjoying its flavor), may hold up down to as little as half an inch.

In most cases a cigar will "turn" at about the last inch-and-a-half to an inch, but again, it depends on the flavors you're getting out of it. Once a cigar goes bitter on you, regardless of at what point, it's best to give it a few more puffs just to make sure it's not going to improve, then put it out.

Finally, the harder and/or more often you draw on the cigar, the faster it will turn stronger or bitter. Let the cigar "smoke itself" by taking slow drags about once a minute.

IMO, the reason many cigar smokers continue to stick it out with a bitter tasting cigar is simply because they want to get every penny out of it, especially if it cost $5 or more.