Lyric discussion by rosidinthebagonger 

Cover art for Lost lyrics by Linkin Park

The song tells about a person who had trauma from past event. Despite he/she tried to ignore the pain, it always be there and never recovered.

@rosidinthebagonger Or (just my opinion), It's about how he or she remembers about the good old days, a massive trauma occured and changed everything, the only light that he has is the good time when everything was okay