Stranded on a Island

Three women, a blonde, a brunette, and a redhead, were stranded on an island. The brunette looked over the water to the mainland and estimated the distance to be about twenty miles. So, she announced that she was going to try and swim back.

After swimming five miles or so, the brunette began to get tired. However, determined to keep at it, she kept going. Unfortunately, ten miles out, she became exhausted and drowned. The redhead, who was stronger than the brunette had been, decided to give it a try. After getting out about ten miles or so, she too began to get tired.
Just like the brunette, she was determined to keep going; only five miles from the mainland, she too became exhausted and drowned.
Now, the blonde had always been the strongest of the three. And so, after seeing how far the redhead had gotten, she knew that
she had a good chance of making it. The blonde swam away from the island, and was making good time. She passed ten miles easily; however, when she reached fifteen, she began to get tired, too. But she kept going.
Finally, after reaching nineteen miles, with the mainland only a mile away and in sight, the blonde realized that she was simply too tired to go on. So she swam back.