What makes a song classic?

The single most thing that makes a song classic to me is that "feeling" you get when you hear the song years later. Kinda like a good memeory it always takes you back and allows you think and fall into that good space. No matter what is going aorund you, hearing that opening horn, voice, note, drum, scream whatever it may be takes you into another place and allows you to escape for 2 minutes.