Why don’t I dare to curse on the street?

That's very good. Not speaking loudly in public places is a sign of politeness and cultivation, and is not directly related to timidity.

Don’t worry. If you are robbed on the street, you will be brave enough to shout out. That is a human instinctive reaction. Maybe you are louder than those who usually chirp.

Don’t envy those who use foul language. It is a sign of guilty conscience and a lack of self-cultivation.

But for normal communication, don’t be afraid of others hearing you. If you have a shy personality, you should also correct it appropriately.

Being upright and sunny is the true nature of a man.