smoking without having consciously decided
Hal finds himself taking the proffered duBois and smoking dope in public without even thinking about it or having consciously decided to go ahead.
Context
The line crossed by nobody: minutes after resolving against exactly this, Hal takes the joint "without even thinking about it or having consciously decided to go ahead" — the distaste and the resolve simply bypassed, the hand moving before the will engages. The habit's signature is that it does not require a decision; the moment the secret user swore off arrives and passes without a self to say no.