What happens when you say set x to x + 1?
You might think of it terms of lerp(start, end, percentage)
Where the percentage is expressed in terms of 1 to 0.00, and 1 is 100 percent.
In this case the percentage is not as important as what is changing in the start. The percentage is the time element, usually expressed using delta time.
lerp(self.x, touch.x, 1*dt)
In this equation self.x is always changing, and so does touch.x, if you move the touch, but self.x only goes to a percentage of the distance between self.x, and touch.y, as long a the percent is within the range of 1 to 0.00.