The Director should ask a player to make a test only when the player’s hero attempts a task where the consequences of failure are interesting or dramatic, and where failure won’t grind the story to a halt. For example, if a hero wants to leap over a waist-high wall while casually walking through a peaceful city neighborhood, the worst case for failure is probably that the hero falls on their butt, takes no damage, and can stand up to either try again or walk around the wall. As such, no test is required. But if the hero were being chased by enemies, failing to leap over the wall means the pursuers can catch them, so the Director might decide to call for a test to determine what happens.
The advancement of a story shouldn’t be halted by failing a test. For instance, the heroes might need to know the color of a dwarf king’s crown to solve a puzzle, with that puzzle opening the only entrance to a tomb they must enter to stop a world-ending ritual. It could be that a successful Reason test allows the heroes to recall that lore, but the test shouldn’t be their only option to get the information. If the test fails, perhaps the heroes need to go to a flying library to do research, or they might be able to delve into a ruin to find the ancient monarch’s portrait. A failed test should always result in a story becoming more interesting, not in the action coming to an end.
It Just Works!
When a hero attempts to solve a task that typically requires a test with clever, outside-the-box thinking, the Director can instead decide that no test is required and the attempt automatically works! For example, if a hero who wants to climb a wall first covers their hands and feet in giant strands of sticky spider webs, the Director might decide that they can climb up the wall without needing to make a test.
That said, such clever ideas often work for free the first time, but the Director could decide they require tests if they are used again.