The proverb that says that "problems are messages" has been attributed in a number of sources to Shakti Gawain. In a book co-written with Laurel King and titledLiving in the Light: A Guide to Personal and Planetary Transformation, Gawain does indeed write as follows:
Problems Are Messages
If there are problems in your life, the universe is trying to get your attention. It's saying, "Hey, there's something you need to be aware of, something that needs to be changed here!" If you pay attention to the small signals, you will learn from them, but if you don't, the problems will intensify until you get the message and start to pay attention.
In other words, rather than viewing problems as entirely negative things, we should instead view them as opportunities to learn and to change. Such a view itself involves a change in the typical outlook of most people, who are unlikely to perceive problems as positive in any way. Gawain's outlook is a version of "the power of positive thinking" -- the idea that we can better deal with problems if we try to approach them with some degree of optimism rather than with a pessimistic point of view.