LSD has quite a bit of subjective experience change based solely on mood, set, and settings. Although beyond that, everyone's reality is not the same as the next guy. Aside from that, repeated dosing of anything at all can be different from dose to dose based on body chemistry, tolerance, hormone balance, and dopamine/adrenaline type of responses. Mood plays a large factor in this as well. Tylenol does not work the same way at the same dose in each and every person, either.
