This is a practical and wise advice. This world demands us to do more. In the process of doing that we will lose ourselves. Multitasking is a necessity in most jobs and that affects our lives as well because we apply that kind of habit and then ingrained to our character.
What multitasking did to me is that I was stressed more than ever trying to meet a lot of deadlines all at once. I failed in most and that has an impact to my self-esteem. I do have issues with self-esteem and that made me look down on myself even more - loser.
Your advice of focusing at one task at a time has been tried and tested. I did that and it made a big impact both at work and myself.
Thank you for your thoughtful comment. Doing one thing at a time has served me well too. Cheers!