I've been welding for 30 plus years, I am a certified welding inspector, certified welding educator, and I'm still learning every day.
The same way I don't believe in faith, I don't believe in mastery. That is a title people with less knowledge "bestow' upon others.
Sometimes when someone is conceited they will use that term. But you will find the exceptional will always strive to improve.

Simply to be happy in my own skin.

There are a few things I could think of, but mastering the art of patience has been an accomplishment for me.

I feel there is no such thing as mastery. Even the best have room to grow

Learning Mandarin. Extremly hard but well worth it.

CPR. Do about a dozen a week at work. (Even though, it's more wearing on my mental well-being than on my pyshical health)

The guitar. I paid for my own lessons with a satuday job at 14. Although after nearly 4 decades I cannot say I am a master of the instument. It has fed me on occasion, provided me with good friends and the odd romance. Now I write my own songs.

I can't say I mastered anything really. Its still work in progress. SWIMMING, WRITING, UNDERSTANDIDNG others, Counselling skills....but after 2 years of personal therapy I can say I accept myself who I am with all my inperfections . It makes me happy?

My first real challenge was swimming, took me a while, well behind others, then suddenly at about 8 I got it, went from my "Beginners Certificate" through to a 1 mile long distance, Bronze Star Life Saving and State Championships before I was 9.
At 30 I couldn't use a computer, never sat in front of anythign like a PC, only computerised terminals. I was teaching computers before the end of the uear and eventually managed a heap of qualifications and jobs in the field. Swimming was essential for my interests in marine biology and surfing, computer games are awesome and I made a lot of money as a systems engineer.

Touch typing. Must have saved me months.

Living in my own skin and being who I am at all times.

I always wanted to learn to play the bagpipes....started with flute in grade school, then piccolo, oboe...finally bassoon in high school...and then, finally, I got bagpipes whilst in college...and NEVER had the time to master them. I still kick myself over that. I can play basic songs...but I'm not a great piper.

As a chef...everytime I mastered some new technique or created a new dish or decorated a super special wedding cake...those were great moments. I also paint...and I remember the first painting I sold. That was weird because I could look at it and see the "mistakes"... I still sell 20-30 paintings a year. But I'm not a great artist. People like my art because it's "happy" and "bright".

Things I worked hard to learn, but love doing it:
1.playing the piano

2.playing electric bass

3.speaking Thai and Japanese, since I learned Spanish, French and Creole just from growing up in Haiti.

4.jumping rope

5.ballroom and jitterbug dancing

6.practiced using a lasso, until I could rope half grown wild boars in the mission corn from my Haitian mustang stallion

7.throwing a knife. I became a deadly aim

8.playing ping pong, until few could beat me.

9.using advanced bird photography equipment

I have not mastered it or never will, but I am trying hard to improve my game of golf. It takes lots of money and hard work, but it is worth it.

The Chapman Stick.....still a struggle

Parts of Myself (never ends lol), Photoshop, Writing, Slowing Down, Cooking, Music Production / Engineering Audio / Acoustics / Songwriting, Breathing, Patience in Adversity, Mediation, Meditation, Turning People's Hate into Love.

Public speaking! I'm no master but I started out not being able to give presentations at work without shaking like a leaf. Now I can speak confidently. It truly can be a learned skill.

Learned to drive a tractor trailer at an early age. Didn't take lessons or any of that. Taught myself. Then learned how to move large pieces of heavy equipment around the New York City, New Jersey, Pa. area and surrounding states. It takes lots of concentration and attention to detail. It ended up being a great career for me, that allows me to live a nice lifestyle. There are lots of trucks on the road, but not lots of specialty haulers.

Muscle isolation in belly dancing.

Loved my Sandsculpture professional for 43 years. At first nobody in my family or friends thought I would survive financial. For the first 10 years could not find another fulltime sandsculptor. GW Bush took away my green card because I refused him a war sculpture. And Trump didn't pay me for a great sandcastle and tried to unionized sandsculptors. You see, when you love your work, you are unstoppable. Over all more happiness than suffering for most wakening hours of my life.

Yoga, though I’m not sure anyone can ever be said to have mastered it. Meditation. And some tantric sex techniques.

My 7th degree black belt was worth the decades of study and effort ... my Ph.D. in math was also worth the time and effort.

art really

Software engineering, wasn't sure at first, now I can't imagine working anywhere else!