If magic were as reliable as materialistic science demands, then it wouldn't be magic but technology. That said, if magic couldn't affect this our "real" world then it wouldn't be real and we wouldn't bother with it. It's that awkward in-between, I think, of effective but not reliable.
For example, one time I had an experience with the paranormal was when I could feel this glow of a symbol through a Christmas present wrapper that told me what it is when I should not have known. I tried to repeat that experience with Zener cards and didn't have any measurable results, not even to prove it to myself. Or, I have out-of-body experiences, but I can't spy on people and say "this happened when I could not have known this any other way" and I can't even say why: the wind in the otherworld is wrong, or I saw an alternate future maybe instead. (As I keep on saying, it's a very silly place.)
Dr. Charles Tart conducted out-of-body experience measurments, which even Robert Monroe couldn't prove even though he joined in and went out-of-body regularly. The only proof was an anonymous "Miss Z" which 1.) is an insufficient sample number, and 2.) is too convenient to a scientist that she is anonymous, even though for a layperson it makes perfect sense that a human being would want to protect their privacy.