I recently attended a workshop on stress where a participant asked if he was better off focusing his attention on one thing or working on several to reduce his risk. His concern was that if he focused on one item that didn't pan out the result could be catastrophic. The other possibility is to have several projects fail for lack of time and resources.
At some level, having multiple projects is unavoidable. We all have multiple balls in the air at once and need to juggle them somehow. Three broad strategies for dong this are diversification, multitasking and task switching. Before I attempt to answer the question, let's take a look at each.
Although the term did not come up in the workshop, diversification is a well understood and appropriate strategy for reducing risk. When your Aunt Louise tells you not to put all your eggs in one basket, she is recommending diversification. If you are diversifying to reduce risk, there are two points you should consider.
First, sometimes people believe they are diversifying when they are not. If you buy three different mutual funds tied to the same index, you've built a modest shelter against something going wrong internally at one of the funds. If the index itself takes a hit, all three funds will suffer at the same time. Diversification can be vulnerable to a common underlying strategy or a catastrophic single point of failure.
Second, successful diversification is a form of insurance. That means it comes with a price. In this case, the price is reduced returns. A diversified investment will pay out less than the best choice among its various pieces would.
By definition, multitasking is doing more than one thing at a time. Some people make great claims for multitasking -- I am not one of them. I limit my attempt at multitasking to listening to audio tapes while walking for exercise or driving. Anything that calls for real attention will suffer from even an attempt to multitask. If you can multitask on things you do regularly, perhaps there's something more useful, more valuable or more important that you should do instead.
Unless your computer has multiple processors and a corresponding operating system, what it does is task switching, not multitasking. Task switching allows one task to complete before focus is switched to another. Tasks for projects take turns. Focus on one item at a time. This is the way jugglers really work and it is your best bet for dealing with multiple demands.
World Class Examples
When Bill Gates and Warren Buffet were asked for the secret to their success, both answered "focus." Your success depends on your ability to focus deeply and switch focus as needed. This is why I think lists of physical actions as recommended by David Allen are so useful. You also get chances to look at the bigger picture, which addresses the one real danger of focus.
The Boiling Frog
You know this story. The key here is to keep an eye on your goal while you keep focus on your tasks. One way to deal with this is to set criteria in advance so you know when to let go. It can be a delicate balance. Many goals fail just short of completion, but goals and payoffs need to make sense. Building a bridge can be great, but building a bridge to nowhere is pointless.