A problem sprouts its ugly head when we ignore doing something we know we should. We sweep something under the rug and a couple of steps down the road, a problem pops up.
A challenge is an obstacle we meet when moving towards something exciting, worthwhile. A challenge forces us to grow, stretch, and change, and when we do, we gain wisdom, experience, and an opportunity.
A lot of people try to avoid problems by avoiding challenges, but the people who take on challenges have the least amount of problems.