I think it’s partly because so many things are made up in life, but time, while relative, is real. As we begin another trip around the sun at a fairly arbitrary benchmark that should probably just be exactly at a solstice, we semiconsciously remember we only get to experience so many rotations before we die, and we hope to make the best of our lives, and we like baby steps, so we say “i will make these changes within my control and this one will be better”