It's because, while the Law is consistent for everyone, our dominant thoughts (beliefs) are unique to each of us.

And you need to comply with what those unique personal beliefs are in order to "allow" your experience of what the Law brings you.

If you are complying with your personal belief system, that doesn't invite doubt and failure into your vibration...it instead brings you relief that you are complying with your unique view of reality.

For example, if because of some bad experience when younger, someone has developed a mistrust of mainstream medical doctors and will only use alternative health therapies as a result, then for them to seek mainstream medical help for health issues would go against their existing beliefs.

And, for them, that kind of help would probably be of little value and might even be counter-productive i.e. make them more ill because they do not believe they are doing the right thing in seeking mainstream medical help.

Yet, for another person with a positive view of medical doctors, mainstream medical help might be a perfect fit for their belief system and it would prove valuable and helpful.

The truth of it is that neither approach is really doing anything at all apart from allowing each person to align their desire with their beliefs and thereby allowing the full power of the Law of Attraction to activate in their lives regarding that subject.

So, coming to your question, for some people making backup plans would comply with existing beliefs. For others, including myself, they are unnecessary unless they are inspired into place while in a good-feeling mood.

So you can't really generalize because everyone's different and also everyone changes their beliefs throughout their lives as well. Beliefs are just habits of thought and you can change your habits whenever you want.

Summing up then...finding a way to align your desire with your beliefs is key to getting what you want in life. But notice something interesting here...it's about finding a way of aligning with your beliefs only...not about the taking of a physical action itself to bring about the alignment.

In other words, if taking some action for aligning seems like too much physical effort then you can always change your beliefs instead and still bring about that same alignment :)

That's why we spend so much time on IQ talking about belief change...it's usually much less effort in the long run than doing all that physical alignment action stuff, like making backup plans :)