I like to say that reason exists to guard against blind faith, and faith exists to guard against blind reason.

Modernist philosophy generally holds that it is wrong to believe something without proof. For examples of this look at how words like "unscientific" are thrown around to discredit ideas and philosophies. The basic idea there is that if it isn't verified scientifically then it shouldn't be believed.
Yet people who are entrenched in this view point never stop to ask themselves questions like "can I prove that its wrong to believe things which aren't proven?" In short the 'scientific' view point has all sorts of philosophical holes of its own that it tries to get people to over-look by pummeling them with "science".
On the other hand, let me ask you guys who are pro secret this...
If you truly 100% believe and affirm, and visualize that you will gain strength/muscle... but you never actually go to the gym and lift weights.. will you gain strength?
I suspect that most will say no.
All those things do serve purposes, and they do have power, but not necessarily in the way that some people present it.
For example, visualization is helpful as a form of mental practice. The mind drives the body and so it is helpful to practice in the mind, just as it is to practice physically. You have to train your mind, just like you train your body.
Affirmations are helpful because so much of what we do is either controlled or strongly affected by our subconscious mind, and our subconscious mind is, in effect, programmed by the conscious thoughts we dwell on.
I don't deny the possibility of miracles, supernatural, and unexplainable things of course. Those are pretty much a required part of my belief system.