You can't afford to let life push and pull you around. The reason that you do want to think positive is so that you can mentally prepare for the challenges in life. You want to be proactive so that you make better decisions which will help you to avoid some issues and be best positioned to endure and overcome others. Challenges are what makes us grow. Without them we become weak and complacent.
View the challenges and obstacles in your life as opportunities to learn and expand your mind. Shine on my friend and live not in fear. Live in the excitement of progress.