Performing three trials reduces the chances of random error in the experiment. To produce more reliable results there ought to be controlled variables.
Any experimental setup has the potential to contain random errors and variations. You can find and lessen the impact of these errors by carrying out multiple trials, which will yield data that is more accurate and trustworthy.
To isolate the effect of the variable under investigation, hold other pertinent variables constant. This makes it easier to identify the manipulated variable as the cause of changes in the outcomes.