This song's title is a representation of "Half Empty," which was its working title during production. This much has been made known by the band, and is reasonably well known (or at least not obscure) among Tool fans. A personal theory of mine, which seems reasonable but I haven't seen anywhere else, is that the shape of a capital letter H is intended as an image of a glass tumbler half full of water. Using a sans serif font, the two vertical bars of the letter are sides of the glass, and the horizontal bar is the water's meniscus. In the Helvetica-style font used by default here on everything2, the representation is pretty much perfect.

Also, while seeing an allusion to heroin use in the song's title is easy given the band's proclivity toward drug references, the song probably has nothing to do with the drug. While introducing the song at a concert in 1996, lead singer Maynard James Keenan described it, instead, as "... the idea of having an angel sitting on one shoulder and a devil sitting on the other. ... about being very close to someone who is tearing you apart, someone you can't bring yourself to leave, but someone who will destroy you because you can't leave them. It is the price you pay for being close to them; they aren't doing it on purpose: 'considerately.'"

Words above in italics taken verbatim from The Tool FAQ by Kabir Akhtar,