Your friends are better at reporting personality traits linked to longevity than you are yourself.

Furthermore, the personality traits associated with long life are different for men and for women:

Friends did much better at identifying the personality traits linked to mortality, as described in a forthcoming issue of the journal Psychological Science. Specifically, young men who were viewed by their groomsmen as conscientious and open to experience -- these men went on to live the longest lives. Conscientiousness and openness are two of the so-called Big Five personality traits. Conscientious people are dutiful and disciplined and organized and dependable, while open people are intellectually curious and inventive. Men with these two traits lived longer -- or alternatively, those lacking these traits died earlier.

For women the picture was different. High levels of agreeableness and emotional stability -- as identified by their bridesmaids and other close friends -- were most protective over the lifespan. Emotional stability is the opposite of neuroticism -- the tendency toward anger and anxiety and depression -- while agreeableness encompasses cooperation and compassion. These findings must be seen in historical context, the scientists caution: The subjects entered adulthood in the 1930s, when these positive traits were indicative of a supportive and easy-going wife, the emotional leader of the family.

http://www.theguardian.com/commentisfree/oliver-burkeman-column/2015/jan/27/your-friends-know-more-about-your-life-than-you-do-including-when-you-might-die

That’s partly a matter of numbers: 

As in all sorts of other contexts, you’re better off asking the views of several people and then averaging the results, rather than relying on just one. (The researchers concluded that this was indeed the main explanation for their results.) 

But these findings are far from the only indication of how little we really know about ourselves or what’s best for us.