When a situation is risky or one isn't sure whether things are going to be OK, one might say that a situation is "touch and go". What is the origin of this phrase?
touch-and-go can mean
"risky; precarious" or "hasty, sketchy"
Etymology Online suggests:
Touch and go (adj.) is recorded from 1812, apparently from the name of a tag-like game, first recorded 1650s
Another version from Loose Cannons and Red Herrings, by Robert Claiborne states:
TOUCH AND GO
Meaning: A risky, precarious situation
Origin: “Dates back to the days of stagecoaches, whose drivers were often intensely competitive, seeking to charge past one another, on narrow roads, at grave danger to life and limb. If the vehicle’s wheels became entangled, both would be wrecked; if they were lucky, the wheels would only touch and the coaches could still go.”
A far more authoritative answer from user Ken Greenwald on the wordwizard forum explains more with examples, quoted verbatim:
TOUCH AND GO is used as both a noun and adjective (‘touch-and-go) and means a precarious situation in which the outcome is doubtful or extremely uncertain for a time – a close flirtation with danger or disaster. “It was touch and go after his surgery, but he pulled through.” “He was familiar with the touch and go of guerilla warfare.” It also has a second meaning of ‘quick action or movement,’ “One must learn to deal with the touch and go of city traffic.’
The first appearance of ‘touch and go’ in a literal sense was in the 16th century (see quote below) as a verbal phrase (used as noun or adjective) meaning to touch for an instant and immediately go away or pass on; to deal with momentarily or slightly. In the early 19th century the phrase took on its two other figurative meaning – 1) adjective:  Involving or characterized by rapid, slight, or superficial execution; sketchy; casual, careless; instantaneous; expeditious. 2) noun:  precarious situation.
The familiar sense of ‘precarious situation’ originated in the early 19th century with reference to coach driving or ship pilotage and appears to have been a literal allusion to a vehicle barely escaping collision. Coach drivers used the term ‘touch and go’ for a narrow escape after the wheels of two coaches touched in a near accident – the wheels would TOUCH, there would be a moment of extreme anxiety, but neither vehicle was stopped, and each could GO on. For sailors a ship was said to ‘touch and go’ when its keel scraped the bottom without stopping the boat or loosing a significant amount of speed. A second nautical use referred to the practice of approaching the shore to let off cargo or men, but in an attempt to save time and avoid the involved procedure of stopping – not stopping. It has been speculated by some that the great risk and uncertainty involved in this maneuver spawned the expression.
Quote: <1549 “As the text doeth ryse, I wyl TOUCHE AND GO a lyttle in euery place, vntyl I come vnto to much.”—‘First Sermon Preached Before King Edward VI’ by Latimer, page 26> [[literally, touch on and go away, deal with momentarily]]
<1655 “Howsoever we may taste of it to bring on Appetite, let it be but a TOUCH AND GO.”—‘Healths Improvement’ by Moufet & Bennet (1746), page 59> [[literally, touch on and go away, deal with momentarily]]
<1812 “There is an art of writing for the Theatre, technically called TOUCH AND GO. . . indispensable when we consider the small quantum of patience which . . . a London audience can be expected to afford.”—‘Rejected Addresses, or the New Theatrum Poetarum’ by H. & J. Smith, preface, page 11> [[figuratively, superficial execution]]
<1815 “'Twas TOUCH AND GO—but I got my seat.”—‘Letters on Epistles to the Romans’ by R. Wardlaw in ‘Sketches of Life’ by Alexander (1856), vi. page 166> [[figuratively, precarious situation]]
<1832 “Free to introduce anecdotes, quotations, and all such TOUCH-AND-GO things as the formality of an essay would not admit of.”— ‘Memoirs, Journal, and Correspondence’ (1854) by Thomas Moore, VI. page 247> [[figuratively, superficial execution]]
<1887 “She caught [the horse]..by the mane, and though it was TOUCH AND GO she managed to retain her seat.”—‘Cleverly Won’ by H. Smart, ii> [[figuratively, precarious situation]] (Facts on File Encyclopedia of Word and Phrase Origins, Facts on File Dictionary of Clichés, Picturesque Expressions by Urdang, Brewer’s Dictionary of Phrase and Fable)
I think it might be related to a touch-and-go aircraft landing. http://en.wikipedia.org/wiki/Touch-and-go_landing