It’s because you assume “Event Begin Play” continue to run after game starts.
Remember, all the red node only fire depends on the condition it listed, Event Begin Play will only fire once when you load the level, and won’t run again.
If you change Event Begin Play to Event Tick, which will run your branch check every frame.
And if later on you know how to do custom events, you can only fire a custom event when setting your pawn’s health, and then check if the value is larger than say 50, if so, fire a custom events.
Thus you will only fire one event when the condition changed, not check health/score every frame.