Learning to fish
The kayak is similar because as you paddle you have the same momentum as the other boats. However, when you get a strike, you stop paddling, lose the momentum and then, as you strip the line in, the boat is typically light enough to start turning towards the fish, thus increasing the chance for slack line. Adding more fun, are the piles of line that are being stripped in the boat increasing the chance that the line will catch on something if the fish takes a big run.
Needless to say, there is a lot going on when you kayak fly fish. In later posts, I will offer more tips on how keep those lines tight.