What does the below image rebus riddle means ?

Solve the puzzle by telling what does below picture means.

A thief enters a store and threatens the clerk, forcing her to open the safe. The clerk says, “The code for the safe is different every day, and if you hurt me you’ll never get the code.” But the thief manages to guess the code on his own. How did he do it?

When I got four, I have it none.
When I got two, I have it some.
When I got none, I have it all.

What is it?

The more you take me, the more you leave me behind.
Who Am I?

How can you take 2 from 5 and leave 4?

What can go through glass without breaking it?

What common phrase is represented by the below lines

Easy going:
Weak, 'I'm going.'
Tough, 'I'm staying.'

Medium going:
Weak, 'I'm going.'
Tough, 'I'm staying.'

Tough going:
Weak, 'I can't do it, I'm staying!'
Tough, 'Let's get going.'

The following "Brain Bat" means Slow Down.
S
L
O
W

Using the same logic, can you tell us what does the following Brain Bat means ?
E
V
I
G

Can you fill the blank with the correct number?

6 30 870 756030 _____