Some take their word more seriously than others. Some think this is about telling the truth or lying. But it is much more than that.
Some are careful with the promises they make. Others can easily go back on promises just on convenience basis.
Some are concise. If he says it is true, then it better be true. Others will shrug and say: “sorry, I thought it was otherwise.”
Some will only say something that will contribute positively to the situation. Others say things for fulfilling the ego. To feel superior; better, stronger, faster. It is always a comparison, and a race: About money, fame, possessions.
Some are careful about what the effect of their words have on others. Others will say the first thing that comes to their mind.
Some pick the words carefully, so they do not take them back, or regret saying them. Others will let anger and fear take control of their words.
No one is on one side all the time. We are humans and we are affected by our surroundings. However, there are norms and averages. On average, where is your word? Are you on the “some” side or the “others” side? On average, can I take your word for it?
How to Deal with Difficult People 