"To Be Or Not To Be, Thats The Question" What Do It Means?

It means that the question is not about doing, its about becoming. 

If you do a crime then you become a criminal - by definition. If you are thinking about doing something bad then what you are actually thinking about is becoming bad. 

Don't misdirect yourself by thinking that a criminal is one that habitually do a crime. A criminal is one that do a crime, even if its once. A habitual criminal is a level up, he is a criminal as well as one that do crimes out of habit. Note the extra adjective: habitual, it comes in addition of base adjective: criminal. You do crime once and you are a criminal.

Whatever you do sticks to you. It becomes part of your personality. It changes who you are. 

Even if its a one-off thing its not done-and-gone. It changes you because next time its easier for you to do it. You are not the same person as you were before doing it because now your personality has changed. Your internal resistance towards doing it is reduced. 

You have also learned to do it by experience. You now have memories about it, memories just not in brain but also in muscles. Next time you can do it little more absent-mindedly. 

How to reverse it if you have done a bad thing? Repent to clean your heart. That may change back your personality but you should do even more. You should start doing the opposite, do good things, and atleast thrice of them. This will flood your brain and muscles about memories of them. This will, hopefully, dilute the influence of the bad thing you did earlier.