Should you have a back-up plan? Yes, if you are installing an update to your accounting system . Not having a back-up plan to pay or send bills if your update goes awry wouldn’t be worth the risk. Even if you executed your back-up plan too early probably it wouldn’t have long term consequences.
But if we are talking about the pursuit of a life-dream, the answer is more difficult. I would suggest that having a back-up plan can create a situation where it is easy to become overly risk adverse. Change is difficult and frightening whether you are changing yourself, your team or your entire organization. In order to succeed you need to plan, deliver, execute and persevere. Going in with a ready made plan to bail out will present too much temptation.
Should you have a back plan? Not if having a back-up plan makes it too easy to give up when the going gets tough.