mercury regularly discriminates..

Yes or no..Good or bad.. Success or no success..Our budhi or mercury regularly discriminates..

And makes us selective..

But budhi is the son of moon our manas,which is more close to sun..The aatman. So we can follow manas who is our driver and more aatman like than neechey who is more manas like and definitely distant from aatman.

That way better choice of karmas can be undertaken..

This is the reason..Rishi advised us to rely on bhavas than rashi because rashi is rahu+shikhi..A combination of past and future..But bhavas are present..