I agree with the statement that we should finish tasks one by one rather than multitasking. In modern society, people are getting more and more busy so that there seems no time for doing things one by one. However, as I am going to point out, multitasking is not really as efficient as people thought. Thus, finishing a task completely and then begin another is the smart choice.

Admittedly, it does seems more efficiently for people to do more than one projects together, since it may reduce the time for waiting. However, there is never a free meal. The cost of multitasking is that the tasks will affect each other which lead to the significant drop of efficiency. As we know, when people are doing a task, they will follow a  work flow. The logic between step and step is crucial. In contrast, when multitasking the work flow of different tasks will entangle with each other and ultimately lead to the breakdown of logic. Without a proper logic flow, I doubt if one can finish the tasks correctly, not to mention the efficiency. Take myself as an example, I used to do my homework while watching TV. The original purpose is to relax myself without waste my time. But it went wrong. It turns out that I could not focus on my homework anymore and started to enjoy TV programs instantly. 

On the other hand, if you choose to focus on a specific task once a time, you will be free from the difficulties mentioned above. Staying focus will be beneficial since it will train you to think logically instead of fragmentary. One of the great triumph of staying focus is the boost of efficiency. A friend of my once told me the secrete of being outstanding is to stay focus on the thing you are doing now. As a matter of fact, he followed this rule through his life and has became one of the best manager in the company. When he was working, he will shut himself in the office to force him to focus and prevent any form of perturbations. In this way, his efficiency was significantly boosted. 

In conclusion, I think it is better to focus on one project a time rather that doing many tasks at the same time.