simple, useful, and original. It’s easy to come up with a task which is useful and original - just combine existing ideas in a new way, perhaps with some minor

simple, useful, and original. It’s easy to come up with a task which is useful and original - just combine existing ideas in a new way, perhaps with some minor twists. But finding something that’s also simple is hard. Interesting a single task that can’t be reduced or explained in terms of existing tasks. Simple things are often primitive (non-compound) in this way, but I doubt it's a requirement.