Things that make multiple research projects different and single project:
Inertia that sets in once I have spent a few weeks on single one of them. The 'switching cost' seems too high to me, and it leads to not much being done first few days of switching to the other project.
Pressure of producing 'visible' results every few months to keep manager/sponsors happy.
Pressure of keeping up with literature related to multiple topics.
What can I do optimize my work productivity?
So you have highlighted some of the negatives of switching between topics, but you should also consider some positives:
- These projects open up different journals/conferences/spaces/collaborators to work with, which is always nice.
- It can help prevent burnout. If you're sick and tired of working on the same thing day in, day out, you can switch for a little while to freshen things up.
- It can actually boost productivity. If you've hit a wall with something, or it's just going to take a long time for the first project to finish, you can switch for a little while and let the previous project cook on the back burner while you get something else done.
There's definitely a time management problem, and it is occasionally a hard one, but working on a single project puts all your eggs in one potentially failure prone, potentially exhausting basket.