My favorite word is "Yes." Every positive experience in my life is the result of Yes. My least favorite word is "Never." Never is the refuge of despair, of ignorance, of a lack of creativity, and a lack of adventure. Never is a word whose existence makes no sense. edit: Follow up is "Because." Only when used as a sentence or reason.
In improv there's a concept of 'yes, and'. The idea is that, when improvising a scene, the natural tendency is to try to control the flow of the story, especially if you think of something hilarious that needs some set up. You can't do that, because you have to work with your partner, you are not in sole control. If you keep trying to force your idea of the story, you break the flow and ruin the whole thing. The way to work around this tendency is to force yourself to always accept whatever the partner gave you, and build upon it - no matter if it goes in a completely unexpected direction. So, if your partner says "and then, we walk into the bar and see an octopus", you don't say "no, actually it was man in octopus costume", you say "yes, and he was the best damn bartender I ever saw". I think the principle applies to everyday life as well :)
John Lennon went to an art show once and told his friend that he didn't want to go but that he would go, look at the first piece and if he didn't like what he saw he would leave. The first piece was a ladder that you could climb and at the top of the ladder was a magnifying glass hanging from the ceiling. When you looked through the magnifying glass you saw one word on the ceiling. The word "yes". He stayed. It was Yoko Ono's show.