The High Aldwin
Good question. I think 5e is loose enough that for players that will depend almost entirely on
whether GM & player expectations match.
As GM, the system expectation that "everyone rolls, no one quits" - that you don't need Proficiency to make a check - somewhat clashes with my own expectations. So I'll quite often rule that a check requires Proficiency. One reason for this is to reduce the number of people rolling.
I agree. The only times we require proficiency is 1) in aiding another to grant that person advantage and 2) if the knowledge/task is truly obscure and would unlikely be covered by general knowledge or experience gained in life. There are some skills I wouldn't think you could attempt without proficiency, such as knowledge skills. But this is where my understanding differed from the designers as Baba helpfully pointed out. This is a derivation from most game systems in the past IMO.
So, in 5E, a character with an INT 16 would get their +3 to any INT-based skills, such as Arcana, but a character who selected the skill and has proficiency in it has actively dedicated additional time in studying Arcana. With further thought, this works out fine really. I've always considered myself a very smart person, and having participated in several I.Q. tests and other measurements of knowledge and reasoning, etc. I am comfortable in claiming I am well within the 3rd standard deviation above the norm. I've picked up a LOT of obscure knowledge over the years and my keen memory allows me to recall most things easily. I've never studied many subjects, but my exposure to a good education, world-experiences and such gives me a deep knowledge base to draw from. While I would most certainly have proficiency in "Arcana" in modern terms, I wouldn't in Religion for example. Still, I know a lot about many religions just due to picking up knowledge about them over the years despite never "studying" them. I would certainly defer to others who have made it an effort to actively learn about Religion, which is why characters likely will defer a skill check to the character with proficiency over the character without.
I am very glad Baba pointed out that difference in game design concept and from a design aspect hobbyist myself it helps me wrap my head around what the 5E designers choices were.