Do you like to multitask, and find it hard to stay focused? This will help right away.

Multitasking, you think your brain can do multiple things at once, but that's not actually true. In practice, it switches at lightning speed from one task to another. That's why it feels like you're doing several things simultaneously.

Every time you switch, your brain stops working on one task, resets itself for the other task, and then has to switch back again. In effect, your brain has to keep figuring out: where was I, what information do I need for this, and what was my intention again?

That costs more energy than you realize.

Joshua Rubinstein and his colleagues call this "switching costs" in their research. After switching tasks, you need more time to respond properly. As tasks become more complex, these switching costs increase further.

But something else happens when you keep switching for a long time.

In an experiment by Monicque Lorist and her colleagues, participants performed a task for two hours in which they constantly had to switch between two different assignments.

At first, participants could still use the time between two tasks to prepare well for the next one. But as they became mentally more fatigued, this became increasingly difficult, and they made more mistakes.

So your brain can still know what it needs to do, while it becomes increasingly harder to prepare itself again for what's being asked of it next.

That also explains why you can sometimes feel quite exhausted at the end of a workday, even though you don't feel like you did anything exceptionally difficult.

You started, got interrupted, jumped in somewhere else, and then went back again. Every time, your brain had to figure out again where it was and what was being asked of you.

If you want to hold your focus longer and not be completely exhausted by the end of the day, don't just look at how long you work, look especially at how often you switch. Multitask in moderation, with these three tips:

1. Does this really need to happen right now?

Ask yourself that question the moment you want to do something in between. If the answer is no, leave it and bundle similar things like email into one moment.

2. Make it easy to pick back up.

If you do have to stop, write down: "When I come back, my next step is…" That way, you won't have to figure out again later where you left off.

3. Give your brain real rest.

During a short break, don't automatically grab your phone. That doesn't give your brain rest, it gives it new information. Step away for a bit, move around, or look outside.

So your focus doesn't just get tired from what you do, but also from how often you change direction along the way.