You can’t simultaneously say “aim higher on the margin” and “aim lower on the margin”, but you can say “don’t aim too high” and “don’t aim too low”—or more simply “mind your aim point”. It is entirely possible that people miss on both sides and they are simply not being careful enough to avoid either extreme.
Consider it a recommendation to be aware of the trade off, not a recommendation to bias your decisions in any particular direction.
You can’t simultaneously say “aim higher on the margin” and “aim lower on the margin”, but you can say “don’t aim too high” and “don’t aim too low”—or more simply “mind your aim point”. It is entirely possible that people miss on both sides and they are simply not being careful enough to avoid either extreme.
Consider it a recommendation to be aware of the trade off, not a recommendation to bias your decisions in any particular direction.