I don't know what deck you're using, but the RW deck shows a naked child riding a horse. So I see the Sun card with a lot of vulnerability, which can definitely be seen as a warning in the card.
Also, horses classically indicate power and forward movement, so if a person is in a situation where the advice is the Hanged Man, for example, but their opposition is the Sun, the may be yearning to move forward with a situation when they are advised not to.
Otherwise, almost always children are shown in this card, so it can represent naivety, helplessness, or dependency.
I have a sister named Sunny Jo - and she is one of those people who says, "I don't believe that all people have darkness in them! I have no darknes in me! Just light, light, light!" But all light is out of balance, and is an illusion.
Think of being in a dark room. When there is no light, darkness is evenly distributed. Now turn on a faint light. The darkness being to gather into "shadows," but you can still see into those shadows ok. Now, turn on a giant spotlight in the same room. Now the darkness gathers into deep, dark, impenetrable shadows. You can never get rid of the darkness. It will simply gather into tighter and tighter shadows. The key is to keep dark and light in balance, so that the shadows cannot hide truth from your only semi-dilated pupils.
So, all light, all Sun, is an illusion and out-of-balance - shadows will always exist. Remember that the most prominent underlying theme and message of Tarot is balance.