Actually, I came to really, really hate this expression.

In an on-line forum that I participated in long ago, this expression was used constantly by (there must be a name for this, it's so common) the local dominating clique that browbeat, ridiculed and shouted down any dissenting opinions.

Their contention was that no amount of "book learning" or documentary evidence could prove anything, that the only worthwhile way to come by any knowledge was through personal experience, and that any documents that contradicted their personal experience of what worked and what didn't was just flat-out wrong. No one who didn't (in their opinion) "walk the walk" had no right to say anything on the subject, no matter how much documentation they had backing them up.

Well, you've got to respect that, in a way.

Unfortunately, the subject of the forum was not survival, it was history.