Dictionary defines “abundance” as something present in large quantity. But the question is precisely which quantity can be called large; is it hundred, thousand or million?? I have seen people whose family income is a million and still they do not feel having enough. On the other hand, there are some people who earn a few thousand and still feel enough for their living. The reason is abundance is not a state that can be calculated objectively. Abundance is an attitude. It is a subjective feeling. It doesn't depend on the outward availability of resources. Instead it depends on one's own sense of having enough. You can have a little and you may still be satisfied with it. You can have more and you can be dissatisfied with it, as @adoore-eu stated in her comment
you can achieve many things and still be unhappy.
The thing that brings abundance to our lives is not wealth, but there are some positive attitudes that are responsible for creating abundance to our lives.
Contentment is very important for sprouting the feeling of abundance in our hearts. We can never feel having enough unless we learn to be satisfied with what we have in our hands right now. In the greed for more, we undervalue what we already have. We are very unlikely to see any quantity (even very big) as enough. We always look at it as small and thus we never have feeling of fullness. Contentment, on the other hand, let us feel sate for whatever we have. With contentment, the presence of small quantity is enough to make us feel abundance.
Gratitude makes the abundance thrive. When we have something and we are grateful for it, we are likely to find a number of ways to increase it. Gratefulness means that we appreciate and value the presence of the entity at our hand. We are very careful and prudent about it and would never like to waste it. Moreover, gratitude makes us happier and enthusiastic. The positive energy brought to us by gratitude let us acquire more and more. As a result abundance flourishes in our lives.
Sharing makes the abundance flow. Now this is something that may sound strange at first but a deeper thought would let us understand how important it is to share (but not hoard) in order to increase abundance. Amidst the covid period, there was an announcement about a medicine that it was helpful in relieving the symptoms. The medicine is used for treatment of malaria. As soon as the news was live, people started hoarding it. It created scarcity of the medicine. Even those people who had no need of it bought it at a higher price because of the fear that they might not get it when in need. What the result was! People who had the real need of the medicine had to buy it at a very higher rate, even some couldn't find it. The medicine was not scarce because it was in small quantity, but it was scarce because people were not ready to share it.
By sharing what is above our needs, we spread well- being and happiness that returns to us in a bigger amount. Several researches demonstrate that those nations where there is lesser disparity between the rich and the poor (in terms of resource availability) are happier and prosper ones. Moreover, sharing cooperation and trust among the people as a result of which abundance is inevitable .
Conclusion
Abundance is not a state but a feeling of having enough. Contentment helps developing the feeling of abundance in an individual. Gratitude helps creating the abundance. Sharing spreads the abundance to others.