What is the meaning of [Don’t quarrel with your bread and butter]

To quarrel with your bread and butter is the give up your job without
sufficient reason, which is foolish.

> ‘Our new manager’s perfect pig!’ said Janet. ‘Even if I slip out for half an
hour or so to do some shopping, he wants to know where I’ve been and why it
took so long. If he doesn’t change his tune I’m giving in my notice.’

> ‘You might not get so good a position next time,’ advised her friend. ‘I
shouldn’t quarrel with my bread and butter if I were you.’