Memento Mori. This means "remember that death is inevitable".

I grew up in a frugal household as well, and I'm still cautious about my spending but spend more liberally than I used to. Since you're still young (I'm still in my early mid 20s myself), we often don't realize the privilege of being young. I realize that I don't want to be at my death bed at the age of 70 with millions in my bank account unspent. I'll probably regret that I didn't spent more to enjoy life while young.