Stick at
Definition 1 of 2
Pro Tip 1/3Emotional Determination
Conveys a sense of effort and commitment when facing challenges. 
Even though the course was tough, she decided to stick at it.
Pro Tip 2/3Time Investment
Suggests an activity may require prolonged dedication to see results. 
If you want to master English, you'll have to stick at your studies.
Pro Tip 3/3Positive Encouragement
Often used in supportive contexts to motivate perseverance. 
It’s tough now, but stick at it and you'll succeed.