Well, that's your impression then. However, as you correctly pointed out, you are not doing a PhD yet, so you don't know how it's like.
but rest assured, I'm very motivated for my PhD and I will never quit, that's for sure (unless I'm dying before I pass my VIVA).
this however, does not imply that I do not have certain difficult days like everybody else where I'm not motivated and find it hard to get some words written. At least I'm being honest and don't pretend that life is wonderful when you are a PhD student.