The phrase "the hardest thing" is an idiomatic expression that means a task or challenge that requires great effort, determination and perseverance to overcome. It refers to something that is difficult to do because it demands a lot from you in terms of energy, time, resources or mental focus. The term can be used literally to describe the most challenging physical feat someone has ever accomplished, such as running a marathon or climbing a mountain. However, it's more commonly used figuratively to refer to any difficult situation that requires great effort and determination to overcome, whether it is an emotional challenge like overcoming grief or a professional one like starting your own business. Ultimately, the phrase "the hardest thing" refers to anything that presents a significant obstacle in life but can be conquered through sheer willpower and persistence.