Your teachers say, "Talk to strangers, because it's fun, it's interesting, it helps people." And you may say, "But I don't know how to talk to strangers. I'm insecure, I don't know what'll happen." So nothing happens.
Yes, all the most horrible experiences in your life came from people who were once strangers and may still be strangers to you, and all of the best, most amazing, most incredible experiences you had in your life have been with people who were once strangers. When you start in this life, you don't have anybody. They are all strangers. If you have a best friend, that friend was once a stranger. If you have had an amazing experience that you love to talk about, the people in that story were once strangers.
Humans don't do well being alone. One of the cruelest punishments you people have devised for one another is solitary confinement, locking you up alone. If you are not willing to meet strangers, to talk to strangers, you throw away all of the possible experiences you could have had in the future. The amazing, rich, beautiful experiences that you'll talk about for decades, those will almost certainly happen with people who are strangers to you right now. If you stay with the people you know and do the things you know, the experiences you'll have in the future will all be like the experiences you've had so far.
The advice your parents often give you, is "Don't talk to strangers." But no - talk to every stranger you can, sometimes the stranger the better. If you want to be wise: wisdom comes through experience, and you simply don't live long enough to have that many experiences. Every person you will every meet, has been through things and has experience. If you talk to them, even for a little, and get them to describe their most amazing story, you can get a lifetime of experience in just a moment. And if you want to be happy and have fun: everyone out there has a smile, has a happy story, and if you can provoke them to tell it, you've just added to your life and made theirs a little better. And if you want to grow big and strong: you do so usually through adversity, by going through difficult things, but it can take a lifetime of adversity to grow really strong. But every person you meet has gone through adversity, so if you can provoke them to share just a little of the feeling of the strength they got out of it, you can acquire some of that for yourself without all the struggle. And if you want to help people and teach: every person you talk to will give you something new to teach and talk about. And every person will have questions, you can try and help them to find an answer even if you can only think of little things to say. Some of them you will help.
Everyone has insecurity about talking to people, also the strangers you talk to. This feeling can be your friend, it can be a beautiful and sacred thing, a desire to be better and more and to love more deeply, to share and lead and help better. So talk to every stranger you can, because the world is full of amazing rewards and amazing experiences and you do not have time to experience them all. Listen to people's stories, share with them, and you will get much closer to your goals without having to do decades or sometimes lifetimes of struggle to get there. Spend a few moments every day making people smile, brightening their day, and you will brighten your own days in the process.