To be "too smart by half" (also common is "too clever by half") is to be too smart for one's own good, meant either literally or ironically. As an idiom, it is usually sarcastic. The phrase has a wide range of potential uses; for instance, it can mean:
1.) Something so complex that it's self-obfuscating.
2.) A seemingly clever action that is in fact foolish.
3.) Logically accepting something as necessary that isn't.
4.) Overanalysis.
5.) Elitism (see ivory tower).
Caused by overworking the Central nervous system of the brain. Eventually certain parts of the body start to shut down, usually starting with the left foot and working its way up the body. Although T.S.D. is very rare, there have been 37 recorded deaths.
Stephen Hawkings is the most well known person who suffers from T.S.D. (Too smart Disease) Another well know case was Franklin Roosevelt