My daughter often asks for a horse as a gift but i don't think too much on how i might provide that request without reflecting on an experience i had in Colorado on one of my first horse-riding experiences. It was easy to mount and take pictures but once that horse started galloping across the open field i realized that i hadn't really thought much about how to rein the horse in. It was in that moment i realized that i missed out on the most important instruction (from my perspective).
Well, horse riding is in many ways similar to emotional control; it is easier to prevent your emotions from going out of hand than it is from reining them back in once they start 'riding' off into the sunset through the open fields. In the book of John, Jesus was preparing His disciples for one of the most difficult times in their lives with the prospects of persecution and loneliness and it was in that moment that He makes this profound statement "Let not your heart be troubled" (John 14:1). This instruction reveals that we are able to control the emotional states of our lives or to put it more plainly, we can prevent ourselves from being troubled regardless of what situations we find ourselves.
This is somewhat contradictory to common psychology which stipulates that we have no control over how we feel; akin to falling in love. Well, Jesus was teaching that you can and should be in control of your emotions. Our emotions are subject to our thoughts and not our circumstances; it is not what you are going through that effects how you feel but how you think about what you're going through that dictates how you feel. Paul wrote from a prison cell saying "think on [good] things" (Phil. 4:8 Paraphrased) even when you are in the darkest of prison cells. In a couple of verses prior he commands the church in Philippi to "Be anxious for nothing". This is key - be in control of your emotions. He doesn't suggest this not does Jesus in His conversations with His disciples; it is a command to us go get it together emotionally. Do not let your heart be troubled; do not be anxious about anything!
Do you know that whenever you are anxious or troubled about anything in life you are in that moment living in unbelief; it doesn't matter what you call it...you will be (in that moment) in unbelief. Get your emotions in control!