This is common. People compare themselves to others because of vanity and bitterness. Pride? Yes. But I guess the most obvious reason why people envy on other's success is greed. They want to be in the position where they want to experience that feeling.

It is a human nature and a very common trait for people who are evil. They got envy because they want to be in the position. They got envy because they feel they deserve it more than you. They got envy most importantly because they are evil. Their hearts are filled with hatred and bitterness.

Success is defined by a person's hard work and a little bit of luck. If they fail to achieve that, they start worrying on the things around. They wish to be the person as they want, but they fail to achieve it that's why they got envy on people who achieved success in life - simply because they failed to achieve it.

One advice, be passive. Don't dwell on their shits. Focus on your life and they're just a little stumbling blocks that hinders your way. Be focused and stay in line with your goals.