The Marshmallow Test provides interesting anecdotes related to self control and the disastrous effects of lacking it. The main theme is how childrens' self control, evaluated through taking the marshmallow test- forgoing eating one marshmallow for a later reward of two marshmallows- manifests throughout later life.
The problem I have with this book is that the conclusions do not seem convincing, the author constantly qualifies his assessments by saying of course there are cases that do not follow the norm. It also does not get to the root of self-control, it instead assumes the outcome of one test as the baseline. It similarly does not explain the basis of the hot and cool systems, but just takes for granted their fundamentality.
A positive aspect of the book is the conclusion that self control is not innate and can be effectively improved and cultivated throughout one's life. It also shows the enormous and varied ways self control affects one's life. Lastly, It is interesting because it covers a variety of psychological tests that anybody can relate to.
Even if it is not groundbreaking, it is still worth the time to read.