How do you practice tenacity?

I really want to become the best me I can, and if I have understood correctly, I can be just that, by embracing all my talents... and I have plenty.
There is so much things to learn, there is so much things... I'm sorry I didn't learn all these things when I was little. I'm sorry I'm not very tenacious. I would speak fluent Finnish, Swedish, English, Spanish, Italian, French, Portuguese, Dutch, Japanese, Arabic, Latin, Hebrew, German, and several other languages, if I had any more resilience... perhaps that is something I need to practice more, not my skills and talents.

How do you practice tenacity?
How do you get that "not afraid of dying on the treadmill" attitude?
How do you learn not to give in?
I really need that. I could do anything if I had that.

Is it just about attitudes, and if so, which attitude it is? And how do you train yourself not to give in?
Is it about fear?
Or priorities?
What is important? Nothing... I wonder if I had it when I was little, but then something happened that made me give it up... all those years of waiting, all those years of "it's not worth crying, it's not worth taking that seriously"... it's no use to do anything, hang on, be tenacious, because the world is as it is, and laisse-faire attitude gives me more serenity. Now.
But combined with fear, what it created was this magnificent body of 100+ kilos, probably diabetes, sleep apnea, pain, bad condition, bad conscience, neverending hunger...

Why am I eating? Food has become the only luxury from being the only affordable luxury... But they say, no food tastes as good as being slim.

I don't believe I will be able to lose weight. I have been overweight my whole adult life, and I have just been getting fatter and fatter every year, the last 10 years...

22 reasons to never give up
They didn't give up... a list of people who didn't give up and what they did

motivation and the power of not giving up
6 ways not to give up
not giving up quotations

I ate pancakes with syrup yesterday. I don't know why. I was watching some inspirational weight loss videos, and getting prepared to walk to the store to buy some salads... and then I remembered that my husband had intended the chicken to be used to make Chinese food, and I should also buy the ingredients for the Chinese food as well. I don't want that. I want a good salad with a lot of different stuff in, different colors, spenach and tomatoes and paprika and fruit and then piece of chicken to go with it... and nice, light French dressing, so that I get the fatty acids I need...