Try as I might (not) I can only see the young woman
A sizable proportion of the population can see either a young or an old woman. A quite small proportion manage to see other things, like mountains, seaweed, a hen's nest, etc.
Among those people who genuinely only see one image and then manage to clearly see another, some initially have trouble seeing the original image, getting 'stuck' on the new image which seems much stronger. The actual experience of being able to switch from seeing one clear image to seeing a different one is called a gestalt experience. The ability, or otherwise, to see different images given the same stimulus is a measure of one's perceptual flexibility.
If you get the gestalt experience from the image you reveal more perceptual flexibility than if you don't. Some people have to look for a long time before seeing more than one image. It is worth noting that your capacity is influenced by how your mind is cued. For example, if you have been thinking or talking about older people you might be more likely to see an old woman in the picture. On the other hand, if you're a bit of a stud you may only see a young woman.
There are some deep lessons for both life and trading in this.