I, not events, have the power to make me happy or unhappy today. I can choose which it shall be. Yesterday is dead, tomorrow hasn’t arrived yet. I have just one day, today, and I’m going to be happy in it.
Misattributed to host Groucho Marx, it was actually a contestant who said it. Found: http://adamselzer.blogspot.dk/2014/11/tracking-down-groucho-quote.html