As mentioned knowledge of corals before purchase. Sometimes not easy to do when you don't know the coral. Do in those cases always side on caution. When you buy an unknown coral always place low in tank, low light. Until you find out what it prefers.
Even if you purchase a medium light coral, Blasto are low to medium. Place it in low light. Gradually increase it to medium over weeks time. Most LFS do not keep LPS corals under their normal medium lighting. They keep them in low light, sometimes just blues. They look better for sale. Who knows how long the medium light coral was in low light before purchase. Then place suddenly in medium light in your home tank which is what the coral normally likes. But being in low light for months, it is a shock to the coral.