A compass is supposed to set direction and show you where to go. That is very useful if you only know that you must walk in one direction, especially if you don't have any other pinpoints that shows you the direction (for example, if you are out at sea and all you can see is water).
In life, optimism is a great compass, because it will let you see something helpful and useful in all situations. Even when things are against you and life is a struggle, it might become a stepping stone to something better.
Just think about it. If you are to carry lots of bricks, then some will see it as a terrible job and a gigantic struggle, and they will complain.
But, with optimism, you might think of it as a great chance to grow muscles and to boost your testosterone levels. After all, if you grow muscles, your heart will beat faster while carrying those heavy loads, which again will grow muscles, which will decrease stress, and grow muscles. This is a fantastic win-win situations, and as stress decrease, your testosterone levels can grow.
What is your challenge today?