In my family, it is strictly forbidden for any unmarried person to sit at the corner of the table. We were told from a young age that if you do sit at a corner, you will never get married. To this day I can't bring myself to sit at a corner, or let anyone else do so. Is this a Jewish belief?

This belief is widely held, and has been handed down for generations in a range of cultures. If your grandmother is Polish, Russian, Hungarian, Rumanian or Ukrainian then there is a good chance she grew up with this superstition. The fact that many Jewish families originate from those 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 have a logical reason behind them. So if a black cat passes in front of you, we don't believe that means you will have bad luck. But walking under a ladder may bring bad luck, if you bump the ladder and someone falls on you. 

So avoiding ladders makes sense, avoiding black cats doesn't. What about table corners?

An 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 f or 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 lost in between, might have a harder time committing to a relationship. That is a corner you don't want to get stuck at. 

Good Shabbos,