This is true. The fact is, there are many ways to skin a cat...there are may ways to successfully handicap. If one uses too many methods or tries to incorporate too many methods concurrently, whether they are successful methods or not the bettor will likely end up with a coin flip.
For example, in an NFL season a system or trend might be successful in applying to say 50 bets, the rest of games won't apply. Now that system or trend might be right, on say 70% of those 50 bets. Another trend or system that would be successfully applied to a
different set of 50 games might also correctly predict 70% of those 50 bets. Pretty good success rates.
But...if you apply the first system to the second set of 50 games or the second system to the first set of games, you may see only 30% success rate for each.
My point is, over the long haul, it is dangerous to limit yourself to one trend, system, angle or whatever you want to call it. That being said, if you were to incorporate every trend, system, or angle available into your handicapping, you would likely dull if not lose any edge and end up 50-50 in picks and lose money due to vigorish.
Although it should be noted that you would likely gain valuable marketplace experience if you understand how to interpret your results in such case.
I would also say that once your handicapping has reached a 50-50 level, you, as a handicapper, are about to "break on through to the other side." The side at which we, the successful handicappers, make our camp and spend our days.