What is wrong when the leaves of a nephthytis plant stay curled up like new leaves and do not open?

Leaf curl can be caused by a lack of water or too much heat/ sun. Also, specific to nephthytis leaf curling, are infestations of thrips, a small insect. Infested leaves become curled or distorted, with silver-gray scars or calloused areas where feeding has occurred. Thrips can transmit tomato spotted wilt virus to other plants. check local nurseries, greenhouses, or home improvement stores for pesticides to treat thrips.