Accepting that "Life is not fair. It never was and will never be" and that following your heart is harder than it seems.
That people will leave. There will be times in which even when you are present, your presence will not be acknowledged and in your absence, your absence will not be felt. Learn to live with it.
Failure is inevitable and Happens. Never tie it to destiny. The strength of an iron chain is defined by its weakest linkage. So failure defines you. Fail and Fail Hard so that when you succeed you would have learnt how not to fail.
Success greets you in private and failure slaps you in public.
Success introduces you to the world and failure introduces the whole world to you. When you fail, always be strong in heart. You never know how strong you are until being strong is the only option you have.
Learning to Pretend like everything is fine. When life is extremely hard on you and you have to fake like everything is normal and you aren't hurt. And the toughest part in that is smiling before others when deep down inside you know that you are deeply hurt and can't even fake a smile.
Accepting that people always be their original self when you are of no value to them and their lives. It is impossible to change the character of people how much ever you try. Even though you can heat water, it has the property to return to the liquid form again in sometime when allowed to be itself with no external stimuli. Similar is the character of the people.
Never judge others. Sometimes we judge ourselves with our intention and others with their actions. This is unfair. Never judge anyone. You would have been looking at page 765 of their book and have a notion of them, but you never know what they have gone through earlier. So it's really unfair to judge people knowing only a part of the story.
And many more things to come as I evolve in my life.