I wonder....an IDIOM

 At Wonderopolis.com they have a "wonder" a day. Have you ever wondered about:

When Should You Come Out of Your Shell?

 Did you know?

"Have you ever been told to come out of your shell? People sometimes use this phrase to refer to kids who are shy. If you’re shy, sometimes you keep to yourself and don’t interact much with others.
Keeping to yourself is kind of like a turtle hiding inside its shell. Turtles feel safe inside their shells. Likewise, you might feel safe from the outside world when you keep your thoughts and feelings to yourself.
However, we believe most turtles would tell you — if they could talk — that you need to come out of your shell every once in a while. When you do, you encounter the world and meet new friends that make life more enjoyable." From Wonderopolis: Wonder # 776

Reading Class number 2 has been working on idioms. 
What is your favorite idiom? or
Is there an idiom that you use all the time?