If he just told me once to take out the trash, I might be able to get away without doing it. I believe that's what Jesus was doing when He repeated Himself in John 14. I said, don't let your heart be troubled and I mean it. I'm telling you again so you can get it straight. If you understand the way fear works, you can see why Jesus warned us so sternly against it.
Fear is perverted faith.
Just as faith is confidence in God's ability to protect you, fear is confidence in Satan's ability to hurt you. And in the same way faith opens the door for God to bring blessings into your life, fear opens the door for the devil to bring destruction. If you refuse to fear, you can go through trouble without that trouble getting inside you. You can go through it in peace and come out on the other side in victory. He wasn't telling you to ignore the events around you.