Yes, coming up with good properties is a skill that requires practice.
I find that in practice, training that skills also helps people come up with better designs for their code. (And people are even more hopeless at coming up with good example-based test cases.)
Of course, property-based testing doesn't mean you have to swear off specifying examples by hand. You can mix and match.
When you are just starting out with property based testing, as a minimum you can come up with some examples, but then replace the parts that shouldn't matter (eg that your string is exactly 'foobar') with arbitrary values.
That's only slightly more complicated than a fixed example, and only slightly more comprehensive in testing; but it's much better in terms of how well your tests are documenting your code for fellow humans. (Eg you have to be explicit about whether the empty string would be ok.)
I find that in practice, training that skills also helps people come up with better designs for their code. (And people are even more hopeless at coming up with good example-based test cases.)
Of course, property-based testing doesn't mean you have to swear off specifying examples by hand. You can mix and match.
When you are just starting out with property based testing, as a minimum you can come up with some examples, but then replace the parts that shouldn't matter (eg that your string is exactly 'foobar') with arbitrary values.
That's only slightly more complicated than a fixed example, and only slightly more comprehensive in testing; but it's much better in terms of how well your tests are documenting your code for fellow humans. (Eg you have to be explicit about whether the empty string would be ok.)