When is it the right time to resign? Most advanced players know when it is time to resign, but many beginners don't.  What factors do you consider when it is time to resign?
The right time to resign will vary from player to player, even if facing identical losing positions. But basically, the right time to resign is when, despite serious contemplation and effort of thought, you are convinced that there is simply no way to avoid a loss, and in addition you have lost all desire to play the position out. That said, there is nothing more frustrating than resigning prematurely, and a saying I've heard before goes something like "It's better to resign one move too late than one move too early," or "It's never too late to resign."

Some players can feel disrespected if an opponent plays on in what the first player considers a clearly lost position. But of course what one person can see clearly, others sometimes can't (or, not unlike the link above, the player who thinks it is already won might be mistaken). A player has every right to play until the bitter end every game without resigning -- these times can even be great learning experiences, seeing how one's opponent goes about winning a won position -- and I believe it is never disrespectful to do so, provided that the player on the losing end isn't, say, just running out the clock, motivated only by a desire to be annoying and waste the opponent's time.