The law of karma

Difficulties are an essential component of life. It is not possible to have a life free of difficulties. The material world is characterized by the omnipresence of miseries , obstacles and difficulties.
That is not so in the spiritual world.

It is said that once in the material world, the soul is bound by the laws of give and take , in other words, by the law of karma.
This is a world of deficiency, of shortage. In order to get something, you have to snatch it from someone else . That someone else will react, leading to bad consequences for you.
For example, in order to take food you must destroy the lives of plants , so that has a reaction.
In order to consume milk from a cow, you deny the share of the calf. Even as we breathe, millions of microscopic organisms lost their lives , getting sucked into our lungs.

There is no survival in this world without karma and karma essentially involves sin. So, in a way, there is no survival in this world without sinning.

We have been wandering in this universe since eternity, in different bodies. The bank account of our karma, the "give and take" account is hidden from us. If that were not so, we would not be able to live in peace even for a moment.
So, the Paramatma, the witness of all our karma since eternity has so kindly hidden our bank account details of give and take from our view.
So, we get difficulties as well as pleasures by surprise, but as per human nature, we may fail to appreciate the good things and complain only about the sufferings.