He told Inside United: "I think it's a hell of a game now. The first thing is to make sure you keep your principles, no matter what. No job is worth it if your pride and your principles are stretched to the limit.
"Once the job starts to impinge on those two things, you need to decide whether you're in the right game.
"The problem is, football is steeped in most managers' blood. They've been in the game since they were kids, they all want to stay in the game and their dreams are still there, so that's what makes it difficult.
"When I started out I didn't have any money, so sticking with your principles is difficult when you've got three kids to feed, but it's still so important."
Ferguson points to Kevin Keegan and Alan Curbishley who left Newcastle and West Ham respectively because they disagreed with what was going on at the clubs.
He said: "Look at what happened with Alan Curbishley - he did the right thing by walking away, and Kevin Keegan, which was a similar situation.
"There's only so much you can take. At the end of the day you're not the manager any more - I don't know why they employ them in some situations."