Definition from Wiktionary, the free dictionary
Alternative forms 
Etymology 1 
- Presumably from trying to guess with second sight.
- (idiomatic) To attempt to predict or anticipate. (Can we verify(+) this sense?)
- 1957: "As a practical matter, a fertilizer company could not afford to second-guess the Federal Trade Commission or a jury in a triple damage case on so obscure a point." (U.S. Senate)
- 1995: "MacGregor avoided this trap by refusing to give managers reporting to him the opportunity to second-guess the solution he would be most likely to choose."
to attempt to predict or anticipate
Etymology 2 
- Presumably from trying to improve with a second stab.
- (idiomatic, US) to vet or evaluate; to criticize or correct, often by hindsight, by presuming to have a better idea, method, etc.
- 1946: "I suppose anybody who keeps a diary and subsequently goes over it for publication has a tremendous temptation to second-guess and make himself look like an oracle."
- 1959: "Public administration would be hamstrung if courts were free to second-guess reasonable administrative decisions." (U.S. Court of Appeals)
- 2003: "If you suspect you've stepped over the line, ask a few other copy editors to second-guess your headline." (Editing Today)
- Please don't try to second-guess the procedure that we have already refined and adopted.
- Once she began listening to her instincts and didn't second-guess herself the entire time, her artwork improved noticeably.
Related terms 
to vet or evaluate