You must know the old trick of cheering yourself up: Turn that frown up side down! For some reason, faking a smile makes a real psychological change. Kind of like how it's tough to be absolutely serious while shrilling "wheee!!"
These simple examples of how self deception, which is often perceived as a negative trait, can achieve beneficial psychological modifications. I want to take this thought a bit further and see how self deception can work to our advantage at work and in life. Let's start with a metaphor
The rider and the horse
Imagine a rider on a horse, surrounded by a great open field. They have a shared goal; crossing the field and reaching the town that's beyond the horizon. The rider knows the way, and the horse has enough stamina to carry them both there. So with the rider's direction and the horse's galloping accordingly, they will soon reach their goal.
That is, if the rider is knows the way, the horse is obedient and they both have faith in each other. Weaken any of these component and the results are somewhat less certain.
In this metaphor, the rider represents our conscious will, or the deceiving self, and the horse represents the underlying mind, the subconscious, or the deceived self.
Blinding the horse
You must know the image of a horse with blinders around their eyes. When riding in the city these blinders are used to reduce its field of vision. If the horses perceive the hustle and bustle of the city all around them, traffic, people, constant movement, they easily panic. But put blinders that only let them see the road ahead, and they find it very easy to follow the road, despite the simple fact that the same busy city is buzzing all around them. This primitive yet powerful deception completes the metaphor for the manipulation I am going to suggest.
Blinding the mind
It is by now common knowledge that multitasking is not an efficient way of working. "One thing at a time" is the core advice you'll find in many pop-psychology books dealing with the challenges of staying focused and refreshed during the workday. Turn off your cellphone, close that facebook tab, have only your work in front of you. Those are all important tips, but they only scratch the surface of our tendency to be distracted. These tips deal with helping reduce the amount of tasks the rider is aware of, while what really matters is the amount of tasks the horse is aware of. The rider doesn't need to put blinders on himself when riding through the city, it's the horse that gets easily overwhelmed. Or translating the metaphor to real world terms, you are not only distracted by what your conscious is aware of (blinking phone notification, open facebook tab, etc.), but also by what the mind is aware of (the meeting in half an hour, the upcoming task after this one, etc.).
To unlock the power of "one thing at a time" it's simply not enough to reduce the clutter the conscious has to deal with. The mind itself needs to be distraction free too. While you can't cancel every meeting and assign someone else to do all your other tasks, what you can do is deceive yourself to believe that these other tasks do not exist. Try convincing your subconscious that there's absolutely nothing else that needs to be done, except the task at hand. Just like how you'd wear a fake smile to cheer yourself up, you can tell your mind, "there's nothing else that needs attending to. This is the only thing that we have to do. No other tasks exist". A mind that believes to some extend that it has only a single, clear task it needs to focus on, is prone to achieve higher levels of focus. Of course this is not a cureall for focus issues, but it's nonetheless a powerful solution for a very fundamental problem that most of us run into: The mind operates best when it has only one, clear task at hand, while we operate in an environment that demands many things of us. When we try to keep all the demands in our mind, even if we don't tend to them at once, we still pay a mental task - the mind will tend to process them from time to time, try to solve them in parallel. This can easily lead to a creeping feeling of being overwhelmed. But when we tell our mind that these tasks don't exist, or are not important at all, it will be fooled to some degree, and worry about them less, and thus will divert more resources to what it is you're actually doing.
The gullible mind
The idea of lying to oneself may sound absurd. How could telling yourself something that you know isn't true could have any effect? But self deception is hardly a rare phenomenon, and it is often the case that it's powerfully effective. And why it works can be understood through the lense of the rider/horse metaphor: The mind can be viewed as two entities in a continuous conversation. You are not lying to yourself, you are lying to the other entity that resides in your brain. I like to think that it's not only logical to strategically self deceive, but it is a great example of what the conscious is there for: The subconscious does all the real work of probem solving, but it requires the direction and manipulation of the conscious to do so effectively. Just like how a rider does not actually contribute anything to covering distance (a rider's weight is even a detrimental factor), but no one would expect a horse to find by itself the optimal path from one city to another, even when it's exceptionally trained. The rider's direction is necessary, and the deception is a powerful way to bend the mind to the will of the conscious.