It’s all relative. What may be a good day for you could be a bad day for someone else. Relativity is important to be happy and to be able to sympathise with others, but of course, this concept also plays a large role in physics. Think of the equivalence principle, curvatures of space, and gravity. If these sound a bit complicated, now is the time to delve into the works of Albert Einstein. Check out his academic or more accessible work. Alternatively, you could stop and think about what you already have and know.