Rarity tiers
Cards are grouped into rarity tiers, from common and uncommon up through rare holo and into the modern ultra-rare and secret-rare brackets. Each tier appears at its own frequency, and the rarer the tier, the fewer packs contain it.
A set might contain dozens of secret rares, so even when you hit the rare slot, the chance of it being the specific card you want is small.
Why averages can mislead
A stated rate such as "one ultra rare every so many packs" is an average across a huge sample. In practice, luck is streaky: you might hit two in a row, or open a long dry spell.
This is the gambler’s fallacy in reverse — a pack has no memory, so a bad run does not make the next pull any more likely.
How PackRip models odds
PackRip assigns each set a rarity structure that approximates its real booster configuration, then rolls each pack against those odds. The result is a pull experience that feels close to the real thing, complete with the occasional heart-stopping hit.