And most swimmers don't have equal arm pull. One arm is stronger, pulls harder than the other. And if you aren't paying attention in the ocean, you'll find yourself swimming in circles or at least a pretty crooked line. They are usually between 50 and 150 feet wide and can flow hundreds of yards behind the surfline. They sometimes flow out of large holes not too far offshore.
Rip currents can drag swimmers away from shore.
The best strategy, if you find yourself suddenly caught in one, is to start swimming parallel to the shore until you are out of the rip current. Most serious riptides are only a few hundred yards across at best, and by swimming parallel to the shore, you'll swim out of it. Once you are out of it, you can swim toward shore. If you try to swim toward shore while you are still in a rip current, you'll wear yourself out fighting it and trying to stay afloat. The other strategy is to just call or wave for help.