Imagining your death. :P

But seriously, it's perfectly sensible when remember that i is just the mathematical representation of "left turn", just like -1 is the mathematical representation of "go backwards"-- and as we know, two left turns sends you backwards. So think about this triangle in the following way:

Imagine you are a snail, starting at the origin. Now imagine that you walk forward 1 step along the horizontal line. Then you turn 90° to the left to start walking along the vertical line, but then, because you need to walk i steps along this line you take another 90° turn to the left, which means that you are now walking backwards and you end up back at the origin. How far away from the origin are you? Zero steps.