Having ways to recover those cards you discard or permanents you sacrifice greatly reduces the cost you pay to draw cards
Is the card at a historical high, low, or average
1 mana for a dork tapping for any color is sick, even if paying full price is weak
Although cards like quests and even sagas that tell a story exist, WotC nailed these designs, representing common JRPG and gaming tropes on MTG cards
You can get crazier with cards like K'rrik, Son of Yawgmoth or Necropotence, which allows you to dump your life total and cast cards for cheap, or you can play it safe with cards like Read the Bones or Bitter Triumph
Simply go to the "Offering Rates" button at the bottom left of the screen before selecting a pack to open