Trying to focus can be hard. Especially when you are doing boring tasks that don't require that much thinking. It's easy to let your mind drift away from the current task and start thinking something completely different. Usually it's a good thing. It makes those menial tasks more bearable and helps pass the time.
There are also times when that's a bad thing. If you are doing something that is boring, but which still requires you to be aware of your surroundings it can even be dangerous to lose the focus. Driving is a good example of this.
It's almost easier to get into a proper drifting mode while doing those boring things than it is to do on purpose. Trying not to do anything to achieve a proper state of mind can be counterintuitively worse setting the mind adrift than those boring tasks. You just can't focus on trying to lose focus. It will not happen that easily. You need to distract your mind with something for it to be able to distract you back with all those drifting thoughts.