The greatest danger comes from other people but more specifically people closest to you.
The problem is that we have a desire not to be alone, to commit ourselves to others and have others commit to us. This is likely a product of biology, an emotional instinct. We have a desire to be vulnerable to others. But this is dangerous. Those closest to us can harm us most and statistically they tend to.
Most rapists are not strangers but those we know. Most abuse likewise is not from strangers but from those we know, those we let into our lives.
It is easy to shield yourself from others. Advancements in law and technology allow this. Walls separate us from others. Laws protect us from others. Most legal systems attempt to uphold our privacy, autonomy and property. We are safe from those beyond our walls and beyond our networks. It is those within who can and do harm us most.
The key to lasting and sustainable happiness is understanding that what gives most happiness is personal autonomy and maintaining a healthy distance from others. Even if we are close to others because we seek warmth or intimacy, we must maintain independence.
We must never give those closest to us the opportunity to destroy us. Being vulnerable is celebrated and glorified by the media and culture as romantic love, but really making yourself vulnerable to others is dangerous, the most dangerous thing we can do. Those who open themselves up to others and make themselves vulnerable are almost always taken advantage of and betrayed, and as this happens more and more, they gradually become misanthropic.
Growing disappointment with humanity and misanthropy are signs of maturity.
What is most important is independence and personal autonomy. You can have people close to you, but never get so close that they can stab you. Maintain a healthy distance. Maintain your independence and personal autonomy. Never fully trust anyone.