Submitted by Rabbi Les Leichman on
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This belief is widely held and has been handed down for generations in a range of cultures. If your grandmother is Polish, Russian, Hungarian, Romanian, or Ukrainian, there is a good chance she grew up with this superstition. The fact that many Jewish families originate from these countries may explain why so many share this belief, but it doesn't come from a Jewish source.
Judaism forbids the adoption of beliefs and practices that are not sourced in our own tradition, unless they are backed by logic. So if a black cat passes in front of you, we don't believe that indicates bad luck. But walking under a ladder may bring bad fortune—if you bump the ladder and someone falls on you.
Avoiding ladders makes sense; avoiding black cats doesn't. What about table corners?
Intensive statistical study into the single status of corner-sitters has yet to produce any conclusive results. But using logic alone, one could argue that sitting at a corner may actually make you more marriageable, not less. It depends on your motive.
If the table is crowded, and you choose the corner spot to make more room at the table for others to sit, then you are a great candidate for marriage. Making space for another is the first step in any relationship.
On the other hand, if you sit there because you can't make up your mind which side to sit on, then perhaps this indicates an indecisive personality. Someone who finds it hard to take a position on anything—who is never here nor there but always lost in between—might have a harder time committing to a relationship. That is a corner you don't want to get stuck at.
Source:
Rabbenu Nissim https://www.chabad.org/library/article_cdo/aid/4423165/jewish/Is-It-Unlucky-to-Sit-at-the-Corner-of-a-Table.htm