A pipe dream is a fantastic hope that is generally regarded as being nearly impossible. The term derives from the mescaline pipe, which was popular in the early twentieth century. Such ideas usually need events to flow in just the right direction to be realized, as a plumbing pipe might. The probability of such a course, however, is extremely low. Misconceptions, obstacles unseen by the pipe dreamer, or simple ignorance of any issues involved are often disregarded. Also pipe dream is alluded to by the fantasies (a rather comical, yet popular, example of this is a banana hallucination which regularly gives the opium smoker bad advice) induced by smoking an opium pipe, but this term has been used more loosely since the 1800s.