I don't agree with this statement.There are two reasons.
The first reason is if workers need to do many different types of tasks,they need to learn many different things.Although maybe someone can accept them, I think it will pay lot of attention to do it.If we just do one things,it will be more easy. For instance, our teacher ask me to watering the flower everyday and my parents tell me to cook dinner for they tonight and then do some chores tomorrow and I will do a new things at the third day.Although this is not a good example, you know what I mean.If we need to pay lot of things in different things, it will be better to do just one things.At least you can pay less attention.
The second reason is if you do lots of work, you will not finish very better.But if you just do one things, you can complete it great.In my daily life, my mother always tell me you should focus on one things. But in fact, I did not achieve it. When I was 5 years old,I told  my mother that I want to learn drawing picture. My mother agree with me.But I after one year, I gave up.Because I found I like music. So I told my mother I want to learn playing piano.My mother considered it for a second and also agreed with me.At this term, I kept playing piano for two years.At this time, I said I wanted to learn basketball. My mother think for a while, and said:" Dear, I know you