The main challenge is to understand that nowadays, all Google's officially released updates, are only just on paper, and not implemented as far as any action in Google is concerned. Nowadays, Google's algorithms are so madly "blended" and on steroids, that even Google's own tech team(s) are confused and clueless about Google's algorithms, so they (Google) simply just keep fingering their algorithms frequently, without being able to program their algorithms in any effective manner, and that is why nowadays, people are seeing wild breakdance moves in the SERPs. However, due to Google simply fingering their algorithms frequently, gullible people falsely believe that "Oh, my website plunged due to that recent Google update" !!!. So, in other words, the main challenge now is to understand that nowadays SEO must not be done as per what Google releases as their "official" updates.