Here's why:
* Lie is used to describe something resting in a horizontal position. It is an intransitive verb, meaning it doesn't take a direct object.
* Lay is used to place something down. It is a transitive verb, meaning it needs a direct object.
In the context of challenges, you are talking about them existing or being present, not placing them down. Therefore, "lie" is the correct verb.
Example:
* Challenges lie ahead. (This means the challenges exist in the future).
Let me know if you have any more grammar questions!