Persevering

Success is always on the side of the persevering.

"The Parisian police," he said, "are exceedingly able in their way. They are persevering, ingenious, cunning, and thoroughly versed in the knowledge which their duties seem chiefly to demand."

He isn't very persevering; he only works in fits and starts.

I'm persevering.

We're persevering.

You're persevering.

Tom is persevering.