If the suction on the windward side of the fin is becoming too big, vapour bubbles will be produced and the flow will break down. The consequence is a sudden loss of control. Modern fins and boards have succeeded in reducing this phenomenon. A good fin will mostly signal the approaching spin-out to the experienced sailor thus, he can take the pressure off the rear end of the board and pull it closer to his body.
Some factors that are increasing the risk of spin-out are: