Why is it important to control all of the variables except one in an experiment?

Any given experiment has numerous control variables, and it's important for a scientist to try to hold all variables constant except for the independent variable. If a control variable changes during an experiment, it may invalidate the correlation between the dependent and independent variables.

It’s copied and pasted from google so make sure to put it in your words :)

So you can tell exactly which variable caused the reaction.