Most of the time, when you make a shot, you are not looking at the cue ball when the tip hits the cue ball. You are looking at the object ball. Your ability to do this is your circle of accuracy.

Where you hit the cue ball is very important. Body movement, stroke, bridge, balance are some of the things that can affect your accuracy of hitting the cue ball in the exact spot that you intend. During your set up to make a shot, you should focus on where you intend to contact the cue ball. Your awareness is very important in the success of this operation.
Having the proper tip placement and a small circle of accuracy increases repeatable shot making and cue ball control. Without this, the inconsistenency causes your brain to be confused and reduces confidence in your ability.
Practice is the answer. Take time and deliberately place the tip in position with a secure bridge, good stroke, smooth delivery and your shot making will improve.