If a player has only 4 cards in their main deck when resolving an effect that tells them to look at the top 5 cards (like Promising Future), does this trigger a burnout?

Ruling: No burnout is triggered. You only look at/reveal as many cards as are available in your deck (4 cards in this example). A burnout only occurs if the deck is completely empty when attempting to look/reveal cards.

Nuances:

• When looking at or revealing cards, those cards remain in the deck (they don't move to another zone like drawing does)
• Since the cards stay in the deck while being looked at, the deck is not considered empty during the look/reveal action
• This means you cannot trigger a burnout mid-reveal unless your deck was already empty before starting the reveal