The film begins and end with the death of Robert Angier. In the opening scene we see Angier drowning during a trick and in the end he's fatally shot by Borden. As the theatre goes up in flames., we see rows of tanks with drowned versions of Angier in them, all dead. This shows us that Angier has been literally drowning himself night after night in order to be the best magician in the world - to beat Borden, his arch rival. It also shows us that the pain of his wife's drowning still destroys him to such a degree that he is willing to drown himself night after night. These elements are keys to Angier's character: revenge, love, deep guilt and blame for the death of his wife and power over himself and Borden.
Borden's character is one who simply is willing to keep secrets even to the detriment and death of his wife. His obsession with having an upper hand. Thus when Angier shoots Borden during a trick and takes his finger off it can be seen to represent Borden's stubborness to keep the upper hand even when it's been ravaged by his profession. This connects to his willingness to keep his secret of having a twin from his wife Sarah who kills herself because she doesn't know who she's going to get, the man who loves her or someone who abhors her on any given night.
The prestige is the final part of the trick where the magician brings back the thing that they've made disappear. But what we learn is that these two rivals, in the end, cannot bring back what they want the most: their loved ones. No amount of professional success, fame or beating out the other will ever be enough. And it's proved in the final scene as Angier dies after being shot by Borden, whose brother has been hanged because of Angier.
