How to convince people of the time required to perform PhD research?
I often draw parallels to elite athletes since most people easily realize that athletes need to train and spend much time getting to where they are (and they usually also have some talent for their sport). The point is that to become good one has to spend lots of time and energy training. How easy it will be is unique to each person. Hence, it is also difficult to say how much time and effort each person needs to complete a PhD. Not that one has to be the best, but one has to be good enough to be at the top. Another aspect that I find useful in the parallel is that athletes usually love what they do, and it is an internal force that drives them. I sincerely believe that some such drive is necessary to complete a PhD without having to torment yourself too much.

When trying to explain the time perspective to prospective students the parallel might not be enough and it is usually difficult to make people realize the interest driven part. This is, in my case, due to the fact that people decide on trying to go for a Phd for many different reasons other than just a genuine interest in the subject. I will add that I do not mean such a drive is the only way through but it certainly helps.