Do your parents know best for you? No, you know best for you, and if you don't, you better start making it so.
"Casual sex is all about physicality, not about psychology". Wrong. Casual sex is possible by projecting a personality onto a stranger. When you get to know someone better it's less easy to project a personality on them. You must actually like them for who they are. Casual sex is very much about psychology, only it involves projection rather than actual knowledge of the partner.
Does god exit? No. "God" is an invention of man, held as a belief out of conformity, psychological weakness or lack of critical, logical thinking on the subject.
"Bad guys get away with it". Wrong. Bad guys may not feel guilt, but the way they experience life is influenced by their principles making them less happy or even full of negative feelings toward themselves, the world and other people. Their punishment is a spiritual one - and not in the afterlife. (there is no afterlife).
"Being practical means that I go after the career that offers the most money with the most stability". Wrong - being "practical" is realizing that your life is only worth something by being exiting and happy, therefore pursuing a career that will satisfy and engage you - level of lifestyle comes second. What good is a great apartment if you come home to it unhappy and tired?
"Ah... the ideal life is life without having to work, only sitting in a Jacuzzi and watching TV with my friends". Badly mistaken.
The happiest people are those who engage in the adventure of using their skills to create new things. They can experience pride and satisfaction in their own mind, independently of others - it makes you strong and gives your life a sense of purpose. It allows you to experience that you can do things well, which is fuel for living. True relaxation comes with a productive lifestyle, not without.
"If I lie, I benefit from it and others lose". Other people may lose from your lie, but you will not benefit either. Benefit is not measured primarily in material terms.
Notice that the man of integrity and principles has confidence in himself, while the one that lies and betrays his beliefs is scared of what everyone else would think of him. Which one do you think feels better?
"I am a better person if I give the slimiest sleezbucket the benefit of the doubt". No, that makes you a coward, or conveniently unrealistic, but not a hero.
"Guns create violence". Human beings create violence. The bad ones start it and the good ones use it to finish it. Disarming your self defense will not make an evil man any less evil or more compassionate. It simply makes it easier for him to hurt you. So no, guns do not create violence - in fact, in the right hands they are necessary to fight and end it.
"If I will suck up to a girl I have better chances of catching her romantic interest". Big mistake. No decent person, especially women, likes a groping man. women like men who pursue their own pleasure and pursue it confidently and openly. (No, you are not a sleezbucket to pursue your own pleasure. How else would you rather live, as a slave?)
"Winning always comes at the expense of someone else losing. Life is about hurt others to gain, or hurt yourself to benefit others". This is a common world view and is absolutely false.
Life is best when you are in a win-win situation with people around you: In friendships that provide mutual gain, in a great business deal both sides get what they prefer to have (you get the chicken, they get the cash).
If you are a man of honor and by being yourself you are hurting someone else, then their pain is a result of their own fault - not your creation. Therefore, you do not gain at their expense: You simply gain, and they simply suffer by their own doing.
This concludes my advices for today on common yet faulty beliefs. Hope you found it useful.