I think it would be appropriate to make this question CW...
It is likely that this question will not survive here on MO for long, but I do hope that the community gives it a chance. I also hope to get answers that might help others feeling unmotivated, but in general not discouraged.
Among mathematicians, especially the young bunch (postdocs and beginning tenure track), among many causes for lack of productivity, two seem to stand out most often: discouragement and lack of motivation, or the combination of both. I in particular fix attention on those mathematicians who otherwise are (would be) very productive -- an assertion made plausible perhaps by their previous contributions. I would go as far as to say that many, if not most, of us know of at least one such example.
There are many possible reasons for discouragement, many of which have been discussed elsewhere (I do not intend to give specific references, especially since what I have in mind are such sources as blogs and discussion forms on the internet, including MO). Examples of such reasons are family arrangements, low salary, high stress (publish or perish kind), difficult personal relations with other members of the department, and other (or, very often, any combination of the above).
Let us assume that discouragement is not the problem, but lack of motivation is. Namely, assume our young mathematician is tormented by questions such as:
Who needs this? What is this all good for? (i.e. lack of immediate, appreciable feedback).
There are many mathematicians far stronger than me contributing significantly to the field; what is my work good for? (self-deprecation)
Would I be happier doing a nine-to-five job, getting my six figures, and living a simple, earthly life? Why am I even concerned with all this abstract nonsense? (resentment, retreat)
I don't necessarily have a problem with academia. In fact, I like being in academia. Maybe I should change fields, but I feel I am now so deep into math, that changing now might actually hurt my career. Besides, I know nothing about other fields, and it would take me some time just to get up to speed. What should I do?
I hope my colleagues do not find out about how I feel, as this is rather embarrassing; however, carrying on with my duties (especially research) is becoming more and more difficult. Should I share my feelings with anyone?
My question is, what would you say if the said imaginary mathematician was your colleague and a close enough friend to come and share her feelings with you?