I think it’s about performing from your strengths. As Peter Drucker wrote about knowledge work;
“…a person can perform only from strength. One cannot build performance on weaknesses, let alone on something one cannot do at all”.
It’s a Puritan ideal in our culture that we should always be working on our weaknesses, but no one becomes successful through becoming merely average in areas they are currently unskilled.
An excellent designer is likely to be, at best, a mediocre coder, even with substantial effort, because becoming an excellent coder requires more time and mental energy than a designer should give to anything other than their central craft.