You can do two things at the same time equally badly. How much can you do at a time? How many things and tasks can you do simultaneously? It would be useful to do several things simultaneously, and in this way save time; however, you must ask yourself if it is worth acting this way.
It's likely that driving a car and talking on the phone, reading emails and drinking coffee, watching TV, and talking to the people sitting next to you seem to be the norm because we do not even think about whether it is good or bad.
Yes, some people really do have these "abilities" but have you ever seen Olympians flitting between different sports? Even decathletes do not participate in all competitions simultaneously. Doing one task at a time is not the only thing we'd like to emphasise here. It is also essential to select the things that we should do, i.e., does this job or task have some kind of value and long-term benefits?
The time of crisis is the best time to 'spring clean' in all possible ways, starting from throwing out useless things to letting staff go, from a limited worldview up to quitting harmful habits, etc.
Your work should be so important that you concentrate only on it. The ability to manage life is the ability to manage time. The ability to manage time is the ability to manage priorities.
Therefore, choose the most important things and do them one by one and equally well!