You've got to read secondary sources too.
These have two big benefits.
One is that secondary sources can go after primary sources that you can't. Maybe you can't get your hands on them -- possibly because of translation. Maybe because of time factors, or you don't know how to analyze them. Reading through all the baptismal records of many London churches, and doing a statistical analysis of them -- well, that was the means by which one scholar demonstrated that all the preachers who deplored the May games for their sexual license were, well, wrong. The month in which illegitimate babies were disproportionately conceived was August, not May; May had no more than the average month; and this is shown nine months later by the baptism of the babies conceived then. Even literary sources can be hard to get through. I read a book on attitudes toward children in the first centuries AD, and the author had gone through many sermons on "becoming like a little child" to pick up Christian attitudes. (The favorites, BTW, were not sexually active, not greedy (children, offered a coin or an apple, take the apple), and not class conscious (the children of slaves and the children of the rich play together freely).)
Archaeological evidence even more so. Information on -- this one was interesting -- lead "curse" tablets thrown into the spring in a shrine in Great Britain during the Roman era. These were all done, they found, in very good hand-writing, even though they prayed that the goddess avenge thefts that were very small, and presumably stemmed from the hands of the very poor. Whereupon the archaeologists conclude that it must have been very respectable behavior, praying for vengeance; the poor must have been freely asking the professionals at the shrine to help them do it properly. Good secondary sources, at that, will show how they rebuilt the picture; they will tell you about the handwriting and what conclusions they draw from it.
Indeed, good secondary sources are a good starting point for reading primary source for a given era. The bibliography, the works they discuss in the text, give you a pointer. In particular, it may point you to what is more useful and less -- crackpot in a given era.
And thus lead to their second advantage:
You can read a Victorian work on folklore. But when you run across the grave and repeated comments that this fairy tale is really a solar myth -- that Sleeping Beauty is a solar myth, with the princess representing the sun and her sleep the night; that Hansel and Gretel is a solar myth, with the blond children (who aren't blond in Grimms' story, but ignore that) vanquishing the night and recovering the sun, even though the tale calls it gold; that The Frog King is a solar myth -- you may wonder how seriously to take it. There having being crackpots in all generations.
A good secondary source on the subject will assure you that, yes, it was a very widespread belief, held by many of the most noted folklorists, including some whose work has been invaluable. And that it was not so much refuted as overwhelmed by the famous writer who proved that, by the same standards of evidence they were using to prove many fairy tales and legends were really solar myths, it could be proven that Napoleon Bonaparte was a solar myth.
Perspective. Not all secondary sources have it. And because all secondary sources are written, like primary sources, for a purpose, you have to keep an eye out for bias. Unlike the primary source, that isn't even part of the subject matter that you came to learn. But there's no real practical replacement for secondary sources.