Imagine you're holding a glass of water. If you hold for a minute, it's not a problem. If you hold for an hour, you will have an ache in your arm. If you hold it for a day, your arm will feel numb and paralyzed. The weight of the glass doesn't change, but the longer you hold it, the heavier it becomes.
"The stresses and worries in life are like that glass of water."
Think about them for a while and nothing happens. Think about them for a bit longer and they begin to hurt. Think about them all day and you will end up paralyzed, incapable of doing anything.