I don't come here often, but the rolling thread below inspired me to contribute. I paddle both, touring and whitewater kayaks on a regular basis, teach beginnners and sell kayaks for a living.
I have often met the lady described in the (really long) thread below. It seems a bit like the ostrich "it-can't-happen-to-me" syndrome. A beginner buys a kayak, often with the full intent to learn to roll. A lesson is taken, often with no success and the student becomes discouraged. Maybe I don't need to roll. I'll use my paddle float (which hopefully has been practiced at least once), or I'll just stay close to shore. For the first few outings the paddler stays close to shore and has a good time. Then complacency sets in and longer tours are undertaken further from shore. At this point you really need to be able to roll, especially in cold water.
I'm amazed at the solo trips people tell me about, without having any idea how to roll. It took me 3 years of paddling whitewater before I managed to teach myself (from a book!) how to roll. I wouldn't recommend this approach to anyone.
Here's what I would recommend if you don't know how to roll, especially if the idea of rolling causes you concern:
1. - Buy a mask and go snorkeling in a pool, lake, wherever. The idea is to become comfortable under water. It's a big step to realize that you can be under water for a good thirty seconds without feeling discomfort. Once your heart rate can take this sort of experience it's time for the next step:
2. - Find a really good, patient teacher who can not just roll, but teach how to roll. The latter is quite rare in my experience, so shop around or ask your friends for recommendations.
3. - Build up your level of comfort upside-down in your kayak. "Hang-around" and get comfortable for a while before pulling the rip chord. If you find yourself "falling" out of your upside-down craft repeatedly it may be time to add a little foam to increase paddler-to-boat contact and boat control.
4. - Only now is it time to get into the rolling progression and get technical.
At this point you should be able to think about actually rolling, as opposed to thinking about how scary it is to be upside down in a kayak. It's a comfort thing, and as in all phobias you can overcome panic by slowly increasing your exposure to the feared element or situation.
It's a comfort thing, and yes, it's all in your head!
One caveat: Plan "B"
Even if you have a 100% reliable one-handed roll on both sides it is still usefull to replay the "what-if" scenario. I still dress for imersion, carry rescue gear (float, pump, flares etc.) and rarely paddle alone, even though I've had only one swim in the last 7 years of paddling. Complacency has a habit of biting you in the a** when you're not watching.
Thanks for reading this far 8-)