Being truthful to yourself matters because you cannot live in line with your values if you are pretending to yourself that you are something else. Truthfulness allows you to be honest about yourself to yourself, and to others, and to live a life which reflects that.
What is importance of honesty?
Honesty is the foundation for trust in a relationship, and trust is necessary for a relationship to function and thrive. When you're always honest with someone, it tells them that they can trust you and the things you say. It helps them know they can believe your promises and commitments.
What is truth and why it is important?
Truth is important. Believing what is not true is apt to spoil people's plans and may even cost them their lives. Telling what is not true may result in legal and social penalties. Conversely, a dedicated pursuit of truth characterizes the good scientist, the good historian, and the good detective.