Not conceding

Holding out for hope, even when your deck doesn’t contain any ways out, is understandable, but not conceding is a strategic misplay. A round of Magic has 50 minutes and you are suppoused to determine winner within this amount of time. At the end of the time limit, if you are still playing, then you get a few extra turns. At the end of those turns, the player who won more games in the match will emerge victorious and if it is tied 1:1, the game is a draw. We may almost treat draw as a loss in a tournament play.

When is it right to give up? First, think of your odds for winning the game. Even if they are really low it doesn't mean that you should concede straight away. It is always possible to topdeck 3 times in a row, but when you are far behind and even topdecks won't change the state of board it is time to think of moving on to the next game. Except for saving time it prevents from giving your opponent more information about your deck.
Secondly, follow the clock. You exactly know how much time your deck recquires to win a single game. Bear in mind, that your opponent will probably not act as fast as you wish while he won the first game and there is no much time left. Give yourself at least 10 minutes for a game.

Don't fall into trap of thinking that conceding is weak and not a good sportsmanship. It's about winning the match, not winning a specific game