The wet conditions are difficult to drive in, so understanding why you might be spinning off can help you improve quicker and gain confidence.
With the limited grip drivers face, they need to be careful hitting the brakes too hard when inexperienced as this is the most common area where a driver loses control. Most newcomers use the brakes like they do in the dry and as soon as the rear brakes begin to lock up, the driver holds the brakes on until they spin; either into the gravel or until they have lost control and facing the wrong direction. If you do lock the brakes and start to lose control, I advise drivers to slowly release the brakes to allow the wheels to turn which will keep the kart facing in the right direction.