What is the meaning of the sentence?

Question

In about good habit & bad, I run into the sentence like

Doing something over and over again until you don't have to think about it is how actions become habitual in the first place

Could you explain more easier expression?

Answer 1

Adding the appropriate commas clarifies the sentence.

Doing something over and over again, until you don't have to think about it, is how actions become habitual in the first place.

Though a much simpler statement would be

Repetition instills habit.

Answer 2

Reforming the original sentence into these two sentences may help you understand the original sentence:

Repetition is doing something over and over again until you don't have to think about it.

That is how actions become habitual in the first place.