Spending your whole life searching? Continuing to search even when your strength is gone and you're about to die? That's perseverance if we ever saw it! The knight's determination in "Eldorado," however, isn't all fine and dandy. In fact, it more or less kills him. And he still never finds Eldorado. Throw that in with the fact that he's all alone, with only a "pilgrim shadow" for a friend, and you've got a pretty unhappy picture of perseverance. A for effort, though!
There's a fine line between perseverance and obsession, people. If one pursues something too aggressively one risks ending up like the knight and missing out on what life has to offer.
Eldorado, shmeldorado. It doesn't matter whether or not the knight actual finds the lost city of gold. It's important that he perseveres to the end.
Almost every line in "Eldorado" is about death, whether it's the knight's approaching death (his strength fails, he must go down the "valley of the shadow") or the death of his dream of ever finding Eldorado. One also feels, while reading the poem, that the knight's whole life has been a living-death. He's so obsessed with Eldorado that he hasn't really lived. Even towards the end of his life—with Death sitting on his doorstep, ringing the bell—all he can think about is Eldorado.
Beware! If we become too consumed with a particular goal, we will end up like the knight, whose life has become a living death.
Death?! Puh-leeze. The knight's dream of finding Eldorado makes him not fear death; or rather, his dream of finding Eldorado makes death seem less scary or less important.
For the first half of "Eldorado," the knight is totally alone. It is only in line 15 that he meets somebody else, and only a "pilgrim shadow" at that. The shadow doesn't seem very real, and it is possible that he's just talking to himself anyway. For all intents and purposes, the knight is alone throughout the poem, and it is implied that he will die alone. His obsession with finding Eldorado leaves him isolated, with only his dreams of Eldorado to keep him company. Super-sad, gang.
Isolation is a form of death. The knight is alone and "alive," but all the shadows in the poem suggest that death follows him everywhere. He's in major need of a buddy.
Careful, Shmoopers! If we get too obsessed with one thing, we end up isolating ourselves and—possibly—dying alone, just like the knight.
In the first three stanzas of "Eldorado," the speaker tells us that the knight has searched for this place for a really long time, but hasn't been able to find it. Bummer. That sure sounds like defeat to us. At the end of the poem, the shadow tells him what he must do, but this ends up just being another invitation to defeat. The poem isn't really about winning then, but about losing. The knight loses in part because he's looking for the wrong thing, but also because he doesn't ever give up—long after he should have thrown in the towel, raised the white flag, and called it a day.
Don't be a sore loser, Shmooper. Sometimes defeat is a good thing, because it makes us try even harder. The knight, after all, is still obsessed with finding Eldorado, even after he has been defeated numerous times.
The knight's quest for Eldorado is kind of ridiculous, which is why he is continually defeated in his search. He's a loser in many senses of the word.