In my experience, reading reliable secondary sources is a bit easier than primary sources. E.g. for philosophy, I read Stanford's Plato encyclopedia of philosophy. For math, I read nlab or Wikipedia. Unfortunately, both of these will require you to be familiar with basic terminology and concepts of the field and that's where most people stop learning at. E.g. I'm a complete layman in physics and want to learn more but the jargon beyond basic mechanics (i.e. velocity, position, acceleration etc) might as well be Greek to me.