Here's why:

* Mercury is an inner planet: This means it orbits closer to the Sun than Earth does.

* Visibility: Mercury is only visible in the twilight hours, either just before sunrise or just after sunset. This is because it's lost in the Sun's glare during the day and not bright enough to be seen against the dark night sky.

To see Mercury, you need to look for it in the eastern sky shortly before sunrise or the western sky shortly after sunset. It will appear as a bright, star-like object.