Stressful
Unlike many of the many whims he enacted in his early cultivation days, Lex was well aware of the dangers he would face by cultivating with dragon fire. He also took into account the fact that the dragon who would be breathing that fire was two major realms greater than himself, and those were two immortal levels!
But he was still confident, and the reason for that was the thorough preparation he had taken for this. Over the past fifteen years, Lex had been focused solely on filling in the massive knowledge gaps he had when it came to cultivation, as well identifying the direction for his future growth.