We have expectations from everything and everyone around us, including our own selves, people/animals/ things around us. 

If these expectations are not fulfilled, we get angry, frustrated, disappointed, and that causes a lot of stress to us. 

But, if we look closely, we and everyone around us, is born here to repay (or reap) karma from earlier life, called Prarabdha Karma. 

That means, the results of our actions not only depend upon the effort we put in, but they also depend on Prarabdha karma that we are living through. In popular terms, this aspect of Prarabdha Karma is called, luck. 

Sometimes, due to the positive aspect of Prarabdha, we get lucky and things work out better than our expectations; while other times, due to negative impact, things don’t work out and we feel unlucky. 

While this Prarabdha Karma is our own creation from earlier lives, we don’t have control over what gets chosen for this life. 

This means, we essentially don’t have control over the results of our actions. We only control how much effort we put into anything, but how things will work out, if beyond us. 

This is the reason, there is a popular Shkola in Bhagavad Gita:
कर्मण्येवाधिकारस्ते मा फलेषु कदाचन | मा कर्मफलहेतुर्भूर्मा ते सङ्गोऽस्त्वकर्मणि ||  (2.47)
We only have the right to put effort, but we are not entitled to results. So, never assume that things we got in life are due to our efforts alone, and never give up putting in efforts too. 

This is the reality of life, the sooner we understand this, the better our life will become. We will stop being angry, frustrated, disappointed, resulting in better overall health and joy in life. 

All the Best!