Sense

Saying No isn't selfish. It shows great strength and courage. You might be in a situation where you feel stucked but afraid of leaving because you can't say NO. You need to protect yourself, set boundaries and choose what matters. 

Say NO:
to that situation that is not good for you,

To that relationship you feel unloved

To that job you feel depressed 

Because at the end only you matters to you

Saying no is very important. It is unwise to keep enduring pain and sadness when you can choose happiness.