Variables are independent if they produce their effects separately from each other. In other words, changing one variable does not affect changes produced by another variable. No matter what happens, you will learn something. Even if your experiments don't answer your questions, they will provide ideas that can be used to design other experiments. Knowing that something didn't work, is actually knowing quite a lot.
Unsuccessful experiments are an important step in finding an answer.
Even so, their results are valuable. Eventually, someone will use their work to find the answer.