Your sewing machine needle is just as important as any other part of your machine. It has to go through the fabric and meet the hook at the right point to create a stitch.
If your needle is bent or damaged the hook can miss the thread and skip a stitch.
Sewing machine needles also have a groove in the front that the thread sits in when it goes through the fabric. You must make sure you use the right needle size for the thickness of thread you are using.
Always be sure to check your needle before starting to sew.