The impermanence of existence must be understood, that all things are temporary, only in existence for a moment, only guaranteed in this moment. All else is not existence, merely a reflection of it.
You have only so much control over your reality. You were born here, you didn't select this life for yourself, you can only deal with the parameters you're given.
The options for what you can do within these parameters are endless. It's your experience, you can alter your perception of it in a million ways, but it doesn't change the nature of the experience itself. The nature of the experience alters how it's perceived.
If you are determined to suffer, you will suffer, but suffering isn't necessary. There's nothing to be gained from punishing yourself for what you don't know, what you once thought, what you've done wrong. The only thing that matters is awareness, total awareness, right now.
This moment exists, and in a moment it'll be gone, completely replaced by the next moment, spent thinking about the last moment, and so it goes on.
Break through the cycle of faulty logic, and engage with reality, right now. Be happy.