There is a considerable difference between being rigid and having some standards. If you have a list of things that you absolutely must have and they are not particularly reasonable (he must be rich, she must be a supermodel), you are setting yourself up for failure. This is when you might relax your standards just a bit. However, having absolutely nothing in mind when there are things that you know would make you happy (she must like my sense of humor, he should be kind and generous) is a total waste of time. Be open-minded but don't let your brains fall out of your head.
We have a saying in the South: “Be particular.” Kate, heed that warning. Whether you are just getting back out there and dating after a divorce or you're out there all the time, having a list of likes and dislikes in mind when dating is very important. If you keep those in mind when you're out there, you might actually get what you want, which is really the point of the whole exercise anyway.