Never leave superglue on the floor.

Reminds me of when I tried to perform a hadoken as a kid.
 
I just didn’t have the lungs to scream loud enough.

@FanOfMostEverything  
There does seem to be some physical link. In Boast Busters, when Twilight lifts the Ursa, her feet crush the ground below her like she’s supporting its weight directly. And in Hearth’s Warming Eve, Twilight magically pulls on Fluttershy, and then Pinkie physically pulls on Twilight, demonstrating that moving the caster also moves the levitated object.
 
But there’s also the time in Crystal Empire when Twilight self-levitates, which is probably a more advanced form.

@gittonsxv  
At the very least, a unicorn gets some kind of sensory feedback from magic. Also, there’s a chance that Discworld rules for telekinesis apply: the leverage is such that lifting something with your mind may push your brain out through the bottom of your skull.

@gittonsxv  
Willpower, maybe. Physical strength, not so much.

this bit was interesting,  
it showed that magic is tied to your physical strength as well as willpower, maybe that is how twilight won that race in fall weather friends.