Carelessness, intentional... I'll never know. What I do know is that staples/tacks are perfect to punch holes in tires. The positive thing is that the air leaked out slowly and I only noticed it when I arrived home! This happened a little while ago already, but I got reminded of it because I suddenly need to use the PC50 again, because my partner is having the car that day. Help me hope it will not rain tomorrow! D: