should you ever resign?

If you're playing in a weekend, 5 round tournament and you're on 3/3, with two rounds to play, and you mess up your fourth game with the last round to be played later in the day, you have to weigh up whether to fight on or resign. If you resign, you may have an advantage in the last round because you aren't so tired as those who had to play 70+ moves in the fourth round. So you have to decide whether your opponent can see out the win. You have to be able to assess the qualities of his play and whether he might be prone to mistakes.

That's something that a beginner won't be able to do, so it makes sense to play on. Also, if you're a beginnner then your opponent won't be strong either and might blunder. So play on in that situation but resign if you have reason to be sure that your opponent will nearly certainly win. That gives you a slightly weaker opponent in the last round and an advantage of not being so tired as other players you may meet in the next round.