There are many variations on the old saying:

The Optimist

'The glass is half full.'

The Pessimist

'The glass is half empty.'

The Engineer

'The glass is approximately twice as big as it needs to be.'

The Scientist

'The glass is full. We estimate the contents to comprise 51.3% liquid and 48.7% air.'

The joke works because we recognize these stereotypes. People are actually like that! The very existence of a word like 'optimist' suggests a personal characteristic and not just a temporary mood. The nature/nurture debate will never be conclusively resolved but experience suggests that much of our individual make-up is what we are born with. It's up to us to make the best of it! Me? I tend to be pessimistic and sceptical, which doesn't sound promising but it has helped me to be a good Project Manager.

Some years ago the Autism Research Centre in Cambridge (England) carried out studies that linked autism with engineering. Among parents and grandparents of autistic children they found a higher proportion of engineers than in the general population. They also found that students of mathematics, physics and engineering had more close relatives with autism than other students did. On the other hand, they found that students of literature had more close relatives with bipolar disorder (manic depression).

Take Risks

I'm not aware of any similar research results about optimisim and pessimism, but there is surely a significant genetic element that contributes to such personal characteristics. But, optimist or pessimist, the important thing is to make the most of whatever we've got. And to do that we have to take risks, try new things. By doing this we can find out what we're good at. We also find out what we're not so good at, which can be painful at the time! In the long run, we can focus on our strengths and not worry about trying to be somebody that we are not cut out to be.

The difficulty for those of us who are optimism-challenged is to take the risks necessary to discover our strengths and weaknesses. It's all too easy to be discouraged by one failure and end up avoiding the next all-important challenge. It's much easier to be happy when things are improving. In the end, the glass appears half full when it has just been poured, especially if there is a prospect of more. It appears half empty when the level is going down.

References

Autism Research Centre 1997 paper
Autism Research Centre 1998 paper