Winners Never Quit
Not everything you attempt can work. If you cannot work out when a plan is doomed to failure and just keep going, that is not the attitude of a winner, that is a symptom of mental illness.
While it can take persistence to succeed, that must be balanced by re-evaluation of your approach and your goals. You need to keep learning.
20 years ago when selling services for my consulting practise, a client, Gerard Fitzgibbon was his name, told me of his three Ps of success.
They were Persist, Persist, P-off.
I have always valued that advice. Persistence is great, and one can even keep going when it gets hard. But also understand when you are simply wasting your time and effort, and choose something else.