While confidence – ביטחון – is good, too much of it can be dangerous. The word for excess, surplus, or over- in Hebrew is יתר (as in אכילת יתר – overeating).
The three letters of יתר form the root י.ת.ר, which is all about what remains – or exceeds the limit. It’s the same root as יותר (more) and the הפעיל verb להותיר (to leave behind/spare). So when you have ביטחון יתר, you have “leftover” confidence that spills over the edge of what’s necessary.
Therefore, overconfidence is ביטחון יתר – literally, excess security.
For example:
ביטחון יתר עלול לגרום לטעויות.
Overconfidence is liable to cause mistakes.
