You might be surprised to hear that mastery is a choice. I know that I was - I had always thought that my talent in maths was a gift. However reading Geoff Colvin's book Talent Is Overrated, I realised on reflection that I had been taught well from a young age and had trained in mathematical methods and puzzles for far longer than my friends at school.
I recommend that you read and buy this book, or even this excellent summary . Many parents have found it invaluable.
So why choose Maths as an option to master? Sport, music, dance and acting already have millions of people willing to devote their lives to it. They are competitive fields. Meanwhile Maths is considered a ‘hard’ subject and you will get a lot of respect throughout school and your career if you are excellent in Maths. More so than most other subjects. So it's a good choice, even if it's only to PROVE to yourself that you can choose to be great at your chosen subject.
So that’s your reason.
My reason is that I love Maths and Engineering and I want the world to have more great Engineers, Scientists, Mathematicians and creators of every kind.
I heard recently from a professor of Electronics, that large numbers of engineering students are dropping out, due to their difficulty with the subject. I don’t want you to have that experience. I want you to love the subject you choose to study and I want you to excel in it and bring that experience to the world.
Mastery is not about getting an ‘A’ in your exam. It’s about getting an ‘A’ in your exam, your career and your life.