Does trigger thumb hurt?

Maybe: Triggering of the thumb or other fingers is associated with a greater or lesser degree of inflammation. The more inflammation the more likely you are to have pain. It is not uncommon for triggering, while irritating, to occur painlessly. In some patients triggering is quite painful and this may be a reason to consider surgical release.

Yes: The triggering or clicking is caused by some swelling of the tendon as it tries to slide through a fascial pulley or tube. If the swelling is severe enough, it can cause the finger to get stuck in a flexed position and this can be painful to straighten out. You can try a splint, anti-inflammatory medication or a cortisone injection to treat this.