Wiktionary
vb. (context idiomatic English) Make conclusions before being presented with all the evidence.
Usage examples of "jump to conclusions".
All I'm saying is that no conscientious researcher should jump to conclusions, much less make value judgments about an entire race on the basis of a few weeks spent among one group of villagers.
The former because he had allowed himself to jump to conclusions about this woman before she even came on board, based in part on the way the admiralty had treated him after Rashanar.
If her long years as a surveyor had taught her anything, however, it was not to jump to conclusions without sufficient facts.
I was willing to let people jump to conclusions but reluctant to give them a push.
Stenton was a somewhat imaginative man, a little too prone to jump to conclusions.