Under one's control or influence.
The magician had the audience on a string with his fascinating illusions.
(dated) In a state of great anxiety.
Source: en.wiktionary.orgYour Highness is a juvenile excrescence that feels like the work of 11-year-old boys in love with dungeons, dragons, warrior women, pot, boobs and four-letter words. One of the heroes even wears the penis of a minotaur on a string around his neck. I hate it when that happens. Roger Ebert
You can lead a horse to water, but you cannot make him drink. Or monetary policy is pulling on a string when the economy is strong. That works. But when the economy is weak and you are cutting interest rates, it can be like pushing on a string. It does not work as well. Lawrence Klein
And the world on a string doesn't mean a thing. Neil Young
You can't push on a string. John Maynard Keynes
We all start out so damn sure, thinking we've got the world on a string. If we ever stopped to think about the infinite number of ways we could be undone, we'd never leave our bedrooms. Jonathan Tropper
Our forebears are deserving of tribute for one indisputable reason, if for no other: without them we should not be here. Let us recognize that we are not the ultimate triumph but rather we are beads on a string. Robertson Davies