Henri Poincaré was a French mathematician from the 19th century. He is often described as a polymath, and in mathematics as "The Last Universalist". He made contributions to not just mathematics but also mathematical physics celestial mechanics and philosophy.
Big Idea: Chaotic Deterministic System
Poincaré became the first person to discover a chaotic deterministic system.
A deterministic system assumes certainty in all aspects. It's a concept that looks at events isolated from outside forces. Thus, you are able to predict outcomes with precision. For example, imagine a glass placed on a table. You can safely predict the location of the cup when using the deterministic model because you assume that no one will touch it and no outside event will happen - say, an earthquake.
When something is deterministic, you have all the data necessary to predict (determine) the outcome with 100% certainty. However, in the real world, nothing lives in a vacuum. Complete isolation is unrealistic. There are always external forces that will interrupt the system or an object. Therefore, chaotic deterministic system.
This type of thinking is helpful for two reasons: First, it allows you to think whether something is certain (if you do X, will it always lead to Y?). Secondly, if something is not deterministic, it allows you to spot what are the variables that might influence the system and then slightly better calculate the outcome.