"Felix Felicis work on person who take it first, on others second," Sardonyx explained, taking his seat back on the stool so that he could reach everything he was keeping an eye on. "Two people against each other, both take Felix, neither one get hurt. Both lucky, both stay out of harm. Luck good fortune, not bad, both have good fortune walk away unhurt. One get hurt by other, for him is still 'bad' fortune. Felix no allow bad fortune.
"Theory, anyway," he added, handing Remus a steel stirrer and gesturing to a small cauldron he was closer to. "How supposed to work. I no make rules, I just mix potion. You mix blue one on left. Three time clockwise, slowly."