Insects get to undergo puberty in private, cocooned within a chrysalis. Humans have to do it in public. The biological form is difficult enough, but undergoing one’s scientific puberty is often pretty traumatic too – for both student and supervisor.
Like biological parenting, the start of a PhD studentship requires huge initial investment of time and energy from the supervisor – time and energy that’s lost from their own experiments. As with all investments, the expectation is that it will pay back more in the long run – i.e. when student is working independently. At this point, needs of supervisor and student are roughly in sync – the student-child wants to learn and the supervisor-parent sees the value of an investment. However the supervisor-parent may resent the drain on their time and energy.
In the middle phase, things are more hands-off and optimal productivity is achieved. The supervisor-parent and the student-child are both producing data, so output for the unit doubles. At this point, needs are perfectly in sync, and both are (hopefully) very happy with the arrangement.
The end is the greatest potential source of conflict, as the needs of the two may diverge considerably and the student-child (teenager?) no longer feels dependent on the supervisor-parent.
Publishing work from the project is probably the main source of conflict. The student may require a first-author publication for graduation or for a postdoctoral fellowship, or they may have little interest in publishing at all if they have decided that their future career lies outside the world of academia. Conversely, the supervisor may feel that the work is not ready for publication and is unwilling to submit it to a journal. Or they may want to publish it very much, but are handicapped by the student’s loss of interest.
There’s some possibility too of exploitation. At the end, the supervisor may want the student to hang around as long as possible. By now, they effectively have a postdoc operating on a much lower salary, and with no need of additional training. It’s worth noting too that the current system of determining eligibility for postdoc fellowships and research grants based on the number of years spent as a postdoc offers a disincentive to finishing a PhD promptly. The student’s best interests might be to move on to a postdoc position (or other job) sooner rather than later.
And becoming independent doesn’t just mean becoming capable of working alone. It also means being able to think alone, design experiments, analyse data, produce figures and write papers.
Early on, the supervisor-parent is generally doing the student’s thinking for them – they’re more familiar with the techniques, topic, and the project background. It means that once a student-child is practically competent the supervisor-parent effectively gains an extra pair of hands (but those two pairs of hands are still being controlled by one brain)
Later on, the supervisor may wish to continue to exert a high level of control but this is not necessarily best for the student – especially if they’re planning to go for a postdoc position, where they will need to be capable of thinking for themselves.
As with all relationships, the key to a successful and mutually profitable outcome lies in good communication. But it’s worth remembering that the puberty dynamic often applies – supervisors should remember that their student is no longer the wet-nosed novitiate they once were, and the student should keep in the back of his/her mind that their supervisor may be struggling to clearly see them as the fully-fledged researcher they now feel they’ve become.