Is there a reason for having Plan B when there is Plan A?

Some would say yes there is, what if Plan A doesn't work? 

Have a look at Augusto Pinaud's blog http://augustopinaud.com/%E2%80%9Cthere%E2%80%99s-no-reason-to-have-a-plan-b-because-it-distracts-you-from-plan-a-%E2%80%9D/

Augusto's Plan A was to become a Writer. He left Plan A to the side and decided to go with Plan B, but what did he discover? Plan B might have given him a secure income but there was no deeper satisfaction about it because it simply wasn't Plan A, it wasn't his dream.

Plan B distracted him for some time until he felt the need to fulfil Plan A. He is now living his dream and he is a Writer, he has goals and he is fully focused on his dream because this dream is what he wants to die for.

Are you living Plan A right now or are you settled with Plan B? 
If you are living Plan A do you have a Plan B in mind? If yes Why?

 My inquiry somehow links with Augusto's blog and here is why. When you have just graduated as a Performer some of the thoughts that run through your mind are; Am I going to be successful? Will I find a job in the business? How am I going to support myself financially? Shall I have a Plan B in mind just in case?

Recent graduates tend to be optimistic and work hard towards their dream. They didn't have as much taste of failure as the more experienced Performers in the business. My goal is to keep that fire lightened up in their mind before they change Plan A to Plan B with the first, second, or tenth 'No' that they hear.

I recently did an interview with Tom who works as a banker. We met at the Actors Temple were we did an acting class together.
He expressed how sad he feels at work and that working in a bank isn't something that fulfils him. He said; ''This job is not what I want to do, is just a way of paying the rent and bills; what I really want to do is to be an actor!''. I could feel how passionate he was about acting and how hard he worked in the class to improve his skills.
When I asked him ''So do you have any further plans about acting in the future?'' he answered ''Yes! I decided to quit my job and become a full time actor! I realised that unless I commit to it 100% I'll never reach the standard of actor I want to be.''

Tom chose to commit to his passion knowing that he has to face some concequences. He wasn't afraid to leave his daily job and fulfil his dream! Now he doesn't have Plan B distracting his Plan A but do you think leaving his daily job was a mistake, knowing that he is not an actor with  experience in the Industry?