You can’t be great at one task if you’re constantly dividing your time 10 different ways. Mastery requires focus and consistency.
This 100-Year-Old To-Do List Hack Still Works Like A Charm
Fast Company

The most successful world-class experts are also successful in only one field. This is because they choose one thing to focus on and be great at. How many two-sport athletes are there? Many. How many win MVP awards and are inducted into Hall of Fames in both sports? Very few. Of course there are outliers, but people mainly dominate in only one field.