Do you really have a good understanding as to what happens inside your DSLR camera  
when you click its shutter release button? The mirror locks up, the shutter opens, light hits the sensor, then the shutter closes, and the mirror returns to its original position. Sounds easy, but you may not realize exactly what happens with all the moving pieces involved and how it affects your images and videos.

Once you pass a certain shutter speed, the shutter doesn’t behave the same way by fully opening then closing. Instead, one part goes down and another part follows closely behind it, leaving an open sliver where light can get through to the sensor, a little at a time. (from the slrlounge blog)

Take a look at this very interesting an educational video done by the slowmoguys. They film the shutter mechanism of their Canon 7D at various speed with a Phantom 4k at 10,000 frames per second.