Life is too short to be beating ourselves over the head. We are not promised tomorrow so why do something that you do not love to do? Why stress? Why get angry or not wear a smile? They are apart of life but we do not hae to put so much focus on it.
Unexpected things happen. Learn to not let it phase you for too long and continue where you left off. A way to prepare for it is expect the unexpected. Try to always think 3 steps ahead.