Expectation is a good thing when it's positive, but only when it is positive. Positive things are usually the outcome of positive expectations. A positive mindset means you have to interrupt the thoughts that drag you down. An example of a negative thought/mindset is: Ahh! See that happened because I'm not good enough. That's the kind of thought you need to interrupt with something like: Ahh! That happened but who knows what will happen next time. It's not good to believe in damaging thoughts like the italiced section.
The bold section is the type of thoughts that are better to believe and will make you stronger. The reasons you tell yourself for why things happen are so important. They make up the thoughts of what we believe of ourselves. So instead of: because I'm not good enough try: because I'm learning.
There are no age limits on learning. Instead of fading into thoughts of: I should have known better please know that making mistakes are a part of life. And when things happen and don't go to plan for whatever reason; you are more than entitled to use positive thoughts rather than negative. They will help you grow much more than beating yourself down will.
Everyone makes mistakes. It's just that the people who don't let it affect them move on from it so fast you won't even see it. Because it was just a chink in their armour. They don't let one mistake or even thousands of them ruin their day. No one is perfect, and don't think you ever have to be. You're you because the world needs you. It may not be clear why yet, but it will surely become apparent in time.