You cannot understand others unless you understand yourself. Self awareness and personal insight increases perception and sensitivity towards others.
A way of observing managers who have little self awareness is to look at whom they are close to at work and who they are not, often showing their prejudices in revealing ways.
Take the building of teams. A manager will struggle to build a high performing team if they suffer from PLUS (People Like Us Syndrome), by only selecting people they know from previous circumstances who are facsimiles of themselves, conforming to their prejudices, i.e. if you don’t keep fit you can’t be effective – ‘I run, what do you do?’. These new recruits are also the same age profile, gender, hobbies, personal circumstances etc. This is very sub-optimal. Diverse teams outperform homogeneous ones. Diversity is good for profitability. We are not talking about the political correctness of diversity here, ticking the boxes to cover all the relevant minorities in tokenistic ways, but real diversity; of views, of perspectives, of experiences, of backgrounds, of skills. When these are blended around common purpose, underpinned with mutual respect, team synergies really do become apparent.
Where does prejudice come from?
Experiences forming opinions that, over time, become fixed, containing discriminatory judgements that seems to confirm a discernable pattern of outcome. The problem is once this way of thinking about something is established people become more suggestible to seeing new reinforcing examples more often than contradictory ones, so the prejudice becomes deeper. Referring back to the manager that believes fit people are more effective, the prejudice is that unfit people are ineffective because s/he can cite examples that conform to this particular mental model, but I’m sure you can think of ineffective fit people and visa versa.
Everybody has prejudices; the more interesting thing is to understand why you have those particular ones you have and how they constantly affect your behaviour, either consciously or unconsciously.
Can you manage/change them?
As we age our views of the world can become more rigid, with some (many?) unfortunate people intellectually dying in their 30s but not being buried until many years later. So the key seems to be to continue to seek experiences that challenge your world view. Try to correlate the strength of your opinion on a subject/issue/person with the depth of your knowledge and first hand experience of it, because prejudice’s partner is unthinking ignorance. People who are able to confront and challenge their own prejudices by making themselves more available to new opinions and experiences, combined with a solid knowledge base around the thing in question, keep prejudice at bay, gain greater insight into themselves and consequently grow as people (and managers).
Final point; beware the person who says they don’t have prejudices, because it’s not true. (Is that a prejudice?)