I came across this interesting article at The Thesis Whisperer blog. It starts with the hypothesis being an academic is similar to “running a small, not very profitable business”. This is mainly down to two problems:
Problem one: There are a lot of opportunities that could turn into nothing, so it’s best to say yes to everything and deal with the possible overwork problem later.
Problem two: Since (outside of a teaching schedule) no one is really telling you what to do with every minute of your time, it can be hard to choose what to do next – especially if all the tasks seem equally important.
My personal experience is similar, but also somewhat different.