I feel like BHW, a Blackhat SEO forum should have a newbie registration email which suggests people learn to RANK a KW before they jump into methods. Some methods do not require SEO to work (Media buying and Meathead's method) but most require traffic from SEO.
Everything works. Most commonly people face:
1. Not enough traffic. (SEO, testing and KW Research helps.)
2. Not enough ROI. (SEO, testing and KW Research helps.)
3. Not quick enough. (SEO, testing and KW Research helps.)
4. Not consistent enough. (SEO, testing and KW Research helps.)
5. Ect.
Learn how to rank first. At least people who post "I can't rank" have tried. If you can rank an easy KW, you move to slight competition, then medium, then take a stab at hard.
Methods are work under the same mechanisms. Rank something, offer value to visitors, visitors click on ads/buy products/open content lockers.
The hardest part of this all would be the requirements to be a SEO.
1. Patience.
2. Testing.
3. Self - Motivated.
You must be patient, you must test, and you must be self motivated. If you are not, you will never make it in SEO.
Not rocket science here. The hardest part is trying, watching efforts get wasted, and going back to the drawing board.