Here's why:
* Sirius is the brightest star in the night sky as seen from Earth. It's a binary star system, with the primary star (Sirius A) being about 25 times brighter than our Sun.
* The Sun is our closest star, and therefore appears very bright to us. However, it's not the brightest star overall.
While the Sun is important to us for life, it's just one star among many in the vastness of space. Sirius, though further away, shines with a much greater intrinsic brightness.