When do you give up at something? How do you make the determination to give up?
When runners hit "the wall", they have to decide to stop or continue. That's true of almost any endeavour.
When is enough enough?
When runners hit "the wall", they are hitting a barrier that is determined by their own physical fitness. Training will lower "the wall" and it will soon, no longer be a barrier. It's the same thing with things that need a credential to partake in. If you can't weld, it's not hard to learn how to weld. If you can't drive a truck, it's not hard to learn how to drive a truck. It gets a little more difficult when the credential requires an earlier credential and the investment of money. Then, the person needs to first acquire the earlier credential to qualify to earn the later credential. They also need to arrange to have the necessary money.
Some things are limited by gender, culture, race, religion and status. If you are an untouchable in India or even in Canada, you will encounter members of your own race that refuse you the opportunity to advance. If you are Black in the USA, you most likely cannot finish high school and most likely will not be employed in a status job - if you are employed at all. The Blacks that escape "their place" always are extraordinary at something and even then, there are constant attempts to put them back in "their place" by our society.
Other things are entirely self created. Many people expect other people to want what they want without discussion, reason or benefit. Many people think that "loving" another person means that the other person must "love" them - without discussion, reason or benefit. If you offer no discussion, reason or benefit - you don't deserve having another person accommodate your wants and needs. People need to understand the difference between lust, friendship and love. Lust is "damn I want to fuck that", friendship is you're fun to be with and I trust you with my secrets, love is I'll give anything to make you happy. I've found that even happily married couples don't love each other. They have a compact, an agreement that allows them to live easily together, but neither will give anything to make the other happy.
So, the answer to your question depends on the nature of the obstacle. If you need a credential, the obstacle can usually be overcome. If you want to work in a Sikh Temple and you are not a Sikh - well, you are going to have to become a Sikh. If you want someone to fuck like a porn star - well, you are going to have to convince them that's it's worth their while. And if you want Miss 10 to "love" you Mr 3 - well, you are going to have to convince them that the acting job required is worth their while. It might also be a good idea to understand the Ladder Theory
http://www.laddertheory.com/ Generally, it's fairly easy to get Miss 4 to "love" you Mr 3 - - a little honest discussion, attention and demonstration of why it's worth her while will usually accomplish the task.