Who they're dealing with

A fancy pencil that’s easier to draw with?
You’re great with the one you practice with.

A new application that’s got faster features?
You’re faster with the one you’ve mastered.

A new productivity hack to get more done with?
You’re productive when you’re not busy looking for new hacks.

There’s always a shiny new thing promising to make you better/faster/stronger.

They don’t know who they’re dealing with.