Having a single purpose; hence, artless; guileless; single-hearted.
To succeed in your mission, you must have single-minded devotion to your goal. Abdul Kalam
An attitude to life which seeks fulfillment in the single-minded pursuit of wealth - in short, materialism - does not fit into this world, because it contains within itself no limiting principle, while the environment in which it is placed is strictly limited. E. F. Schumacher
I was single-minded on what I wanted to do since I was like nine or ten. Sam Elliott