up to no good
Like many already said, I think its a great improvement over some of the previous editions (2nd and 3.x). Though, to my players' chagrin, they still fail DC 15 rolls at higher levels and get frustrated by how it breaks their immersion. After all, shouldn't the super smart wizard be able to recall basic arcana knowledge?
5e ability checks: "An ability check tests a character’s or monster’s innate talent and training in an effort to overcome a challenge. The DM calls for an ability check when a character or monster attempts an action (other than an attack) that has a chance of failure. When the outcome is uncertain, the dice determine the results."
Even if there is a chance of failure why is the DC 15 (medium) instead of 10 (easy) or even 5 (very easy) for basic knowledge?
Why are they rolling to recall basic arcana knowledge in the first place?
They definitely needed to include more examples of when not to roll.