In D&D, letting everyone roll perception, investigation, or knowledge checks guarantees success, so why bother rolling?

“They’re invading soldiers, who right now think they can capture and ransom—or plunder the person of—a king.”

I’d like to try out writing but story mechanics are super foreign to me. I have so many visual worlds I’d like to play with but have no clue how to weave a character centered story.

How is the worship of Talos treated in Thay?

Are elves immune to bubonic plague?

I rarely ask *everyone* in the party to make perception, insight, or lore type checks, because someone almost always rolls high. Why bother rolling?