What it means to be sincere...

Never reject someones sincerity.
"we as humans" can grow to be selfish enough to reject the sincerity of others. A perons words that lack sincerity is like a body that has no soul. So when anyone approachs you in sincerity, reply to them with the same caliber of sincerity.

This may be difficult, considering you may not feel the necessity or desire to be sincere; however, there are two ways that "we as humans" can be genuinely sincere, when we might feel otherwise.

1. actively listen to the other persons words; try hard not to think of how you want to respond, but focus on what they're saying (both verbally & physically). Direct your mind to the person speaking and seperate your brain from your personal thoughts & feelings. This helps you see between the persons words which is basically, understanding their sincerity. This is pretty difficult, but it's like anything else....practice will eventually make you a pro at it. But, the better you become at it, the easier it'll be to seperate the person's intentions from their inability to communicate their message (e.g. someone really angry, but just wants to do good).

2. Try really hard not to take anything personal, even if it is directed at you. As in, if someone is terribly upset with you, try hard not to erect a "psychological defense wall" that will prevent you from understanding their message. Even if someone is directly angry with you, humble yourself to listen carefully, even if it sounds like rubbish. You can humble yourself by instantly acknowledging you've done something wrong and by actively listening, you can disect why the person is emotional (or irrational, angry etc.) and this will help you connect with them.

"we as humans" should strive to connect with people on the basis of sincerity. This helps us connect with people on the most "human" level because sincerity is someones desire to be genuine.

We make the mistake of "wanting" to connect with people on the basis of their knowledge, wealth, status and so on. This is selfish and anti-human because sub-consciously we are wanting to "get" something out of them. But ofcourse, there are exceptions.

We cannot engage with people who we think will match or excell us in knowledge, these are the seeds of arrogance and we all know, it is a slipperly slope.

How do we do all this????
It's done through active consciousness. We need to make sure that we are not always acting or speaking on behalf of our habits (which humans portray unconsciously). "We as humans" need to know what our bad habits are. So that when we think they will come out, we will actively engage with ourselves to ensure that we will act according to what we know is best.

Again, there are always exceptions.

Just wishing "we as humans" can act like this all the time.