I've only ever experienced one on a commercial flight, and that was in LAX
in perfect weather.
From a pilot point of view flying a Cessna 172, I've only ever had to do a go around initiated by ATC once and that was because a 757's tail had not cleared the runway in time after it crossed my runway at BFI
. Other than intentionally doing them in training, I've only ever done one because I botched the landing. A crosswind came and blew me too far off of the centerline for me to correct since it was a small runway.
Go arounds can be caused for many reasons. Very often they are because of weather. The winds and visibility may be very close to the limits of what is acceptable and pilots may want to attempt an approach, but may have to abort it if the characteristics get below their minimums. A common occurence is approach into fog since you have to see the ground at a certain altitude (depending on equipment being used) and if the pilots can't they have to abort the approach. Strong crosswinds can cause the same problem. Another cause which isn't as common are mechanical problems. A warning light may go off and cause the landing to be aborted. And finally there are problems daily with separation. Planes crossing runways too slowly, or not exiting fast enough when the planes are stacked up tightly. Furthermore planes sometimes make approaches to the wrong runway. All these can cause go arounds.
If you have never designed an airplane part before, let the real designers do the work!