Well... every experience we have, every feeling, emotion, sensation, perception, whatever, is only and just only a state of mind. We do not percieve the outside world directly, but only the mind states it causes in us. We are only aware of our own mind, nothing else. We percieve the outside world through it, but what we actually percieve is the states the mind are because of the outsides world influence.
So, the real high is the state the mind is when high, and not the mere existence or not of THC into the bloodstream or the brain. The THC itself cannot force anyone to get high, if their mind dont coperate. Its the reason because many newbies dont get high even with consumption of massive doses of THC. Because its their mind that doesnt know how to enter in the "high" state of mind, even if their brains were fully loaded of THC.
Yet, old users can get very high with minimal amounts of weed, because their minds already learned how is to be in the "high" state, so they only need a very little push to get there. Sometimes they can get high even without any ingestion of THC, just by being next someone who is high.
Being high is a state of mind, so its not impossible that the mind itself can make oneself feel high even without any amount of THC in its brain.