[spyglass]

Task-switching has a cost even on computers, and it has a much higher cost to us, because we have to acclimatize and deacclimatize to tasks, both cognitively and emotionally, in order to reach optimum efficiency.

In terms of efficiency, concentrating on one task at a time is best, but as people, we also get bored, and look for amusement/distractions. Other projects are a useful way to cater to this need.

One major/difficult project, and a handful of trivial/noncritical/short-term projects are a good combination. Don't take on more than one major project at a time.