The Law of Reciprocity states that the world gives you what you give to the world. By doing for others you make favorable impressions on them and relationships blossom as you extend courtesy, kindness, honesty, respect, and other favors. Even if favors are small, they accumulate over time, as you build trust and create a history of what to expect from each other.
Some people confuse the Law of Reciprocity with Newton’s third law of motion, where every action has an equal and opposite reaction. Actually the two are subtly different, and the main difference is time. For Newton, every action force is always opposed by an equal and opposite reaction force immediately and instantaneously. There is no delay or latency, and where no external forces are present, the reaction is in a predictable direction and of calculable magnitude.
However, if you give with an expectation of an immediate and equal reciprocation, then you are straying across to Newtonian physics and are likely to disappointed. The principle is that others will reciprocate in kind based upon the way you treat them. People evaluate your actions and motives through giving and receiving, and you may give many times, over many years before you see a return.
Interestingly, the world may reciprocate from a completely unpredictable direction, and may surprise you. If you give to others, with no expectation of direct and immediate rewards then the results will seem almost miraculous and be completely unexpected.
Finally, remember that according to The 7 Spiritual Laws of Prosperity you can’t out give the universe.