If you read a lot of scientific papers, or I guess academic papers really, and you care about where the information is coming from, you develop a habit.

I guess I, have developed a habit. I can’t speak for others but I think it’s fairly common.

That habit is to look for references whenever an assertion is made. There are three kinds of assertions in academic writing.

1. Assertions with references: This is a case where the author has read something elsewhere. Ve wishes to pass that information along to the reader, perhaps to build an argument. A reference shows that the assertion comes from elsewhere, and most importantly, where to find it.
2. Substantiated claims: In the field of science, this would be direct reference to included data (say, a table or graph), or an inference based on such data. No external reference is necessary. The reader may not trust the data, but the experiments should be repeatable by the reader to be considered valid.
3. Unsubstantiated assertions: These generally fall into two categories: (1) Restatements of common knowledge, which one should know or can easily look up in a general reference or (2) Bullshit.

I call the last item (unsubstantiated claims that cannot easily be verified by a general reference) bullshit because without the back-up included in the other case, the reader has no grounds to believe what is written.

Try reading, say, a religious text with this frame of reference. It’s rather illuminating.