Continuity mistake: The view from Monica's apartment changes after the first few episodes.
Continuity mistake: Ross always had an end apartment. At some point in Season 8, his apartment became a middle apartment. In earlier season, when Joey had mistaken Ross' for the hot girl's apartment, it showed the apt as an end apt. In TOW Joey tells Rachel, when Joey asked Rachel to have dinner at Ross' apt, it showed another hallway where Joey came from which is supposed to be the wall/ Ross' kitchen.
Answer: The statements that she's contradicting (that it is common, it happens to every guy, and it's not a big deal), are the things that a woman commonly says to a man who is suffering from erectile difficulty, typically to assuage his bruised ego. However, most men do not believe that these statements are true, as evidenced by Chandler's outburst. He's so caught up in the proof that women are lying about it that he gives himself away.
Rooster of Doom