Marking the Spot

Two friends rented a boat and fished in a lake every day. One day they caught 30 fish. One guy said to his friend:

- Mark this spot so that we can come back here again tomorrow.

The next day, when they were driving to rent the boat, the same guy asked his friend:

- Did you mark that spot?

His friend replied:

- Yeah, I put a big 'X' on the bottom of the boat.

The first one said:

- You stupid fool! What if we don't get that same boat today!?!?