As others have indicated, if you put in the time, the CFA is relatively easily achieved. Where it gets difficult is when the rest of life gets in the way. IMO, if you have 2+ of the following, the CFA program can be a serious strain once you get to level II:
- significant other that is not fully onboard
- kids
- 50+ hour workweek
- can't/won't study at work
- long commute (where you drive/can't study)
- deep commitment to vacations/living life
When in the program, I had young kids, long commute and long work week. Given the demands, I used a weekly review course to keep myself on track. It obviously cost a little more, but I felt I couldn't afford to get behind.
For level II and III, I also took a 3 day crash course through Mark Lefebvre. I don't know that those were necessary, but I happily traded a little more money to ensure I didn't put my family through another study cycle. I fully endorse his program, and would not personally be concerned about his falling out with Creighton.
Level I is pretty easy, was nothing more than a capstone type finance class (undergraduate level). While easy, it is critical to truly learn the material at level I, not simply study enough to pass. Other levels build off the material. Level II is probably most difficult for those weak in financial accounting or math. I didn't have a deep accounting background, so this was where I had to pour in a lot of extra hours (and ultimately decided to use Mark). Level III was fairly easy for me as a wealth manager, as I combine disciplines every day. Those that had a narrow role at work (i.e. a bond trader) seemed to generally struggle a lot at level III.
Before I started each level, I read/worked through a calculator manual/tutorial geared toward the program. I think this was one of the best decision I made and the time easily paid for itself multiple times at each level.
I always kept a "secret sauce" formula sheet with me. Reviewing that regularly helped keep material fresh. That was critical given there will be sections you don't review for a couple of months or more while going through the primary readings.
Don't forget to eat right and exercise. Weakening your immune system and getting sick is very counterproductive to studying.
One final tip... at every exam someone near me had a box of 20 or so pencils they had to sharpen right before the test started. Don't be that guy/gal.