Of course you will fail.
The "Spell" and the "Intent" itself is already your "car", but without a "Gasoline" a.k.a Energy (Psi or Chi Energy) into the spell, I guarantee you that it will not be a spell anymore but a prayer... and prayers are... not always bound to work because it's like asking your mother to make you a cake while not entirely sure if she really wants to make you one (the freewill of the deity on whom you sent your prayers).
So to guarantee the spell to work, you have to do energy manipulation in it, spell casting is more than chanting words vocally or in your head and believing that it will work.
The effect will be similar too:
"Oh, I will have that glass to levitate and go to the water jug and fill it with water" with you just staring into the glass while "believing" that it will work, without you moving your feet to go to the glass and fill it with water, you can stare at the glass forever and have no results while still believing that the glass would float and make it go into the water jug to fill itself with water.
See? Everything is all about energy manipulation, study Psionics, for Magick and Psionics have similar concepts.
Now regarding doubting yourself, it all depends on your brain, all you have to do is become "AWARE" of the existence of magick and the energy you sent into the universe while "programming" that energy to do what you want it to do (that's spell casting on a general level), become aware of them, and tell to yourself that they are natural, convince yourself more of it.
The effect will be:
"Oh, it is possible to walk using my feet... my feet exists so I don't have to doubt myself if I can walk to the place I want to go or not."
In other words, think of magick as a part of you and that it exists in this material plane and everything that happens because of it is real and natural and part of this planet.