be on firm ground

Meaning

1. to be in a strong position in an argument, etc. because you know the facts

   Everyone agreed with me, so I knew I was on firm ground.

In the movies · 1

• I would have stayed on firm ground and let them dare away.Anne of Green Gables1985
• Everyone's to keep their feet firmly on the ground while I take Mr Longbottom to the hospital wing.Harry Potter and the Sorcerer's Stone2001

From the same entry

• a firm hand
• take a firm line
• hold firm
• stand fast
• firm up
• firm up