As noted in another comment, Wait is extremely prone to deadlocks - if you happen to Wait on a thread that's running the event loop, then no task that's scheduled on that loop can execute until Wait returns. So if you're waiting on such a task, or on a task that depends (no matter how indirectly) on such a task, you get a deadlock.

Now, if you're writing a library, you pretty much cannot assume anything about the event loop and what's scheduled on it. If your library invokes a callback at any point, all bets are off, because you don't know which tasks that callback may have scheduled, or which tasks it's waiting on. Similarly, if you provide a callback to a library, you also don't know which tasks you might block by waiting.

So, in effect, the only safe place to wait is on a background thread that was specifically spawned for that purpose, and that is guaranteed to have no event loop running on it.