Why is everything so hard and requires effort?

I understand life is not easy and yes it's unfair but the part I don't seem to understand is why is everything so hard and requires effort. It's always this cause and effect situation. It's easy to gain weight but hard to lose off weight. It's easy to sit in comfort zone because it gives pleasure but hard for the mind to become discipline. In life, if you want anything good whether it's a high paying job then you must study hard to get a degree or really learn a skill to get somewhere in life. It's take long time to build a solid relationship but just minor mistake can break up everything.