Never settling results in better decision making, increased openness to opportunities and ultimately a better outcome. For me, 'never settle' has a few particularly significant meanings.
Firstly, never settling is about constantly striving. That is seeking to develop or improve one's skills in - and a knowledge and understanding of - a particular field. This may range from working to improve one's written communication skills and develop a better understanding of Physics, to attempting to increase the distance one can run. Often, this will involve repeatedly seeking out and attempting to resolve personal shortcomings. This will not only lead you to become better at something, but will also reinforce the importance of hard work and industry.
Secondly, never settling is about being openminded - and not fixed in one's views. In the investing world, where you must have a strong view before you act, never settling is about having "strong views, which are loosely held". This is essential if one wants to be able to evaluate facts objectively and make good decisions.
Thirdly, never settling is about constantly seeking opportunities, and embracing change, instead of becoming increasingly comfortable with the status quo. This may be about being willing to move countries if a better opportunity presents itself, and being willing to seek mentors from different fields, or about choosing to be an early adopter, or even an innovator. This will lead to personal growth.
The 'never settle' mindset is very powerful. Thus, I encourage you to ask yourself what 'never settling' means for you, and I urge you to subscribe to this philosophy.