well, i guess i was lucky i got black rouge and gold monk

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It's just superstition Dong. Random is random, just keep using them as you acquire them. 100 Crystal pieces is 20 rolls, and on average would net you just over 4 silver or better units. The chance of getting exactly a silver from SP summon is very close to chance of Plat Armor from Armor Daily H on Monday for comparison. In three months of using all resources for Monday daily, I've gotten some 0 and 1 days and even got 2 once, except for one random day I got 6. Keep in mind that's without using SC, over half my runs that day dropped plat armor. Run good happens, I'm sure your luck will catch up eventually.