When you say that someone knows their own mind, you are saying that they will not be persuaded to do things they don’t want to do. For example: A parent discussing the safety of their daughter Susan, when she leaves home, might may say “you don’t have to worry about Susan she knows her own mind”. Another example: a parent discussing that their child could be persuaded to do bad things might say “I know he’ll be ok because he knows his own mind” The use of practical in your example is a second and separate descriptor.

“I’m working” Someone usually uses this expression to explain that their time is being paid by their employer right now and so they aren’t free to do personal things, even if it looks as if they aren’t working. Example: you are being paid to deliver something and on your way you bump into a friend, who invites you for a quick coffee. You might say “I would love to, but I’m on the clock right now”

Some examples: The earthquake triggered a fault in the electrical system. The fault triggered a break in communication. After the the faults were found, a response was initiated.