(Psychology Interviews) What is an ideal sample size for an experiment and why?

Rather than declaring a given number as an ideal sample size, it's better to look at what the study is looking for and what type of experimental method is used. For lab experiments looking at the effects of neural mechanisms on eating, perhaps a smaller sample size would be used depending on the budget of the experiment. For an experiment on eye-witness testimony, ideally, a large sample size of maybe 200 would be used due to the significant implications of the results. There is no set ideal number but a larger sample size is always better to increase the reliability of the findings but this may not always be practical.