I have been to resorts where they give you a basic rundown and then let you puddle about in the pool for a bit to get comfortable, kind of just to set you up for the money shot of a resort course or full course. We have some friends that did that in the DR, and decided they then wanted to get full certified. They never regretted it, and the tipping point was flopping around in 4 feet of water in a pool for an hour.
I agree with Harriette. The past two trips did not dive but snorkeled. A lot more work snorkeling, and fun, but it ain't diving.