Lyric discussion by duellynoted 

Cover art for Lightness lyrics by Death Cab for Cutie

ok, i'm gonna go out on a limb here, but i'm going to say that the writer has read The Unbearable Lightness of Being by Milan Kundera.

in the book, a major theme is "lightness": the idea that when we live in such a way that we have little affect on the world as we make decisions. example, if i have no friends, i'm not in a relationship, and i do not keep in good touch with my family, i am light. the decisions i make affect no one but myself. the book is about such a man, named tomas, who meets a woman, falls in love, and marries her. his addiction to women did not hurt anyone when he was single and had severed contact with his ex-wife, son and even his parents, but now that he is married, it hurt his wife. over the course of their marriage, he cheats on her probably hundreds of times and it tears her apart.

the song would fit in well with that. it's about tomas, or someone like tomas, who is tempted to make a decision that will hurt someone. "oh, instincts are misleading you shouldn't think what you're feeling they don't tell you want you know you should want."

i think my theory may be further proved by the song "soul meets body." soul and body were another theme in the book. several chapters were named "soul and body." that being the idea that body wants, even craves one thing, and soul knows better. lightness allows soul and body to be detatched, but heaviness creates conflict between them. when soul meets body is love. all else is meaningless.

incredible book. even if you don't agree with my interpretation, go pick it up and read it. you won't regret it.