Something you may not realise right now is that your mood and the way you act can really affect other people. Not only can it affect their mood, it can also affect their opinion and perception of you.
Even if someone thinks that they won't be affected, it can affect them on a subconscious level, and they might not even realise it.
The way this works, is, when we are with someone, we imitate their body language and facial expressions (this is just a natural instinct), and when we do this, it triggers reactions our mind that lead us to feeling the same emotions as the person we are imitating.
This can reflect both positively and negatively on a person. For example, a happy, lively person can spread this happiness and make others feel good for no specific reason. However, if someone is angry and agitated, this can lead to them spreading this anger and unkindness to other people.
This is why you have sometimes put your emotions into perspective. Just one person can spread so many emotions, whether they are positive or negative emotions.
This is also why you sometimes have to control how other people make YOU feel, and not let their negative emotions get to you. It's just not worth spreading negative emotions to other people just because one person made you unhappy.
People who can control their emotions, and not spread or take in any feelings they don't want are very powerful people, because they are simply unbothered. It is a very useful quality to have in life.
Anyway, I hope this helped, have a nice day, bye!