This is the sentence struture that used to be with me:
If i haven't been so careless, i would be...
If i have attended the activity, i would get...
If i haven't been so impulsed, i would become ...
If i have treasured what i have owned, i would not...
There will be so much if, but life is a ticket without return, there are no so many chances for me to waste. I don't know when i became such kind a person stongly missing the past things and feeling regreted for the missed chances. But until one day, i realize, when i feel upset with someting, i have missed the more important. In future, i couldn't promise miss something, but i will treasure everything. Live for the moment.