This sounds like good advice in theory, but if someone isn't even at the stage of knowing what they want to read, I don't think picking a significant book at face value is going to work out well. In fact, I bet it would probably end with a large majority of people reading the first 10 pages of Plato/Socrates/etc., getting confused by the utter lack of context, and giving up. That's what I did the first couple times I "tried to get into philosophy." It took me getting to undergrad philosophy classes to really "get it."

At the very least, if you're going to go for primary sources, find a guide or lecture to lead you through it. Of course primary sources are important to read in philosophy, but in my personal opinion, I would recommend going for an introductory text first and picking primary sources to read from there.