Don't waste time thinking about what could have been when you could be thinking about what could be.
When the world changes, you have to adapt and change with it. It's not just death and taxes that we can always count on in life.... add 'change' to that mix. No matter what, tomorrow will always be a little bit different than today.
You have to realize what you don't know before you can learn about it.
What if there were no hypothetical situations?
If life was a piece of cake, it wouldn't be worth eating!
Do not kick people when they are down because you will surely fall right beside them.