Brewing the potion itself was also an arguable challenge, since even with the Half-Blood Prince's copy of Advanced Potion Making at hand, Harry noted that concocting his own batch of Felix Felicis was "seriously complicated". And given how Hermione reacted when Slughorn confirmed the potion's identity during their first Potions class along with how inadvisable it is to excessively imbibe it, it can be assumed that the potion was indeed very rarely, if ever, successfully brewed even by skilled potioneers - making Slughorn's ability to do so particularly noteworthy.