I am a great advocate of being positive, but this has to be context sensitive and not simply happy clappy behaviours that quite honestly seem to drive most of our colleagues mad. So, authenticity is most likey the key, and we can probably all relate to people who have 'a nice way about them'.. that leadership thing, yeah, they have that! Two cautions re over-optimism, one which is brought to life in a great article by David Collinson from Lancaster University. He introduces the 'Prozac Leader' and suggests that these leaders often will not consider alternative voices and refuse to concede failure or admit mistakes. The second, and probably most dangerous, is the 'Charismatic Leader,' whom although you distinctly know what they are saying is going to lead to harm, you follow anyway. Steve Kempster and Ken Parry (Lancaster University - of course!) have written extensively about this very subject, viewing it through the lens of the follower .. a caution here would be that it may be unhealthy to fall for your boss! 

Always good to finish with an illustration...!