My first postdoc position  started almost three long years ago. Since then I have come to realise that getting closer to the end of your own research project can be an experience that is not unlike an emotional rollercoaster. As the source of your livelihood for the past 3 years is rapidly slipping away, you may feel dragged suddenly and uncontrollably towards the bottom. On the upside, during these last few weeks before you move on to whatever comes next (for me, like many of us, this will be another inevitably short-term research contract) you surely have moments of intense satisfaction to savour. These moments might just sweeten the bitter taste that the passing of your project into science history may leave you with.
1) You get to wave a final goodbye to those fruitless experimental leads that wasted months of your lab life. The end of your contract is time to discard all that private pain: the frustration that you had to bury just to make it possible to carry on experimenting down some other new avenue. I'm not being overly negative here. Of course, I understand that experimental cul-de-sacs are an inevitable consequence of chasing the unknown and perhaps have their own role in advancing science. Good riddance to them all the same, though.
2) On the other hand, you finally get to nail some of those tail-end experiments that have been flapping around in your mind for months. OK, so these experiments never quite made it onto your 'urgent and essential' list but once done, they will give your project the ultimate polish. Of my short list of must-do-it-sometime experiments, one or two of these date back to the first year of my project, whilst the majority are more recent unfulfilled desires. They all have one thing in common; just a few short weeks left to pour their results into my lab book, my hard drive, and my mind. Miss the boat and they are history. The demands of my next project, which are already encroaching onto my working week, will leave little time for fiddling around with old news.
3) As a direct result of 2) you may now have enough data for one or two short low-impact papers. These will have no great bearing on your future employability but they may rank among your favourite contributions to science, however little they are cited in years to come. Putting them to bed in a low-ranking specialist journal is infinitely preferable to leaving the data to slowly deteriorate on some soon-to-be-obsolete storage medium. This kind of moment has also enormous potential to help you face the end of your contract with a good feeling about what you have achieved, even if that isn't as much as you would have wished back in the heady days of year one.
4) You now have the ultimate excuse/motivation* to tidy up. If you don't give your lab space a final clearing-up session you risk someone else discovering just what a messy worker you were as they sniff around your former freezer drawer for anything worth pilfering. And you don't want to give people any reasons to be bad-mouthing your work. So let's be kind to our colleagues and leave behind flat surfaces and empty drawers. Well, at least as close to flat and empty as you can get without your lab mates feeling that your scorched earth policy means you must be covering your tracks in some way. We´ll just call it good housekeeping.
Also, if you don't clean up yourself it is highly likely that someone else will throw away months of your work, so they can have the unusual and not unattractive plastic box you kept it all in. OK, you may never have wanted to use these samples again anyway, but you may feel less emotional about their loss if you've given them the death sentence yourself.
Even if your next contract is in the same lab, this is still a good time to have a good clear-out. Keep only what's worth keeping lest you get clogged up. 'It might come in handy one day'. Yeah, right!
5) After you have experienced the joy of moments 1) to 4) your life will be relatively free of heartache, must-do experiments, and lab clutter, at least for the few days until you get stuck into your new project. Well, apart from the bit of forward planning that's doubtlessly already going on in the suburbs of your mind. But the downtime between projects is a rare and precious momentary mental freedom. And while we scientists are paid to fill our minds to the brim with amassed knowledge and new ideas, there is probably no better way for a scientist to reflect on their science than being disconnected from it for a while.
So, wallow in whatever sense of achievement you can find. Your project may have been a record-breaking ride with more ups than downs, or it may have been a disappointing little merry-go-round. Either way, you stayed on to the bittersweet end and did your job. So feel good about yourself before you queue up for the next scary postdoc ride.
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* Select the applicable term, depending on whether you are a compulsive minimalist or die-hard hoarder.