Sometimes saying no to others means being true to yourself! I used to be terrified of saying no or expressing my honest opinion. I had to learn that saying no means being honest, being real and being selfish (but not selfish in the negative sense we tend to attach to it. Selfish means carrying about yourself, loving yourself). Think about every time you say yes just because someone expects it from you. So what if you don't agree with everything your colleague or friends say. This makes you a person, someone who has an authentic personality, someone interesting. Think about it, would you rather talk to someone who agrees with every word you say or someone who has their opinion, someone who would tell you honestly the things as they are?