I only wanted to get married once, so when I felt I was ready to handle it, I looked at my relationships and noticed that boyfriends get tired of girlfriends, and vice versa, but you never get tired of your friends.
The idea that a war can be won by standing on the defensive and waiting for the enemy to attack is a dangerous fallacy, which owes its inception to the desire to evade the price of victory.
A trip to space is a big motivator to give up some things in your personal life. Obviously, you can't give up everything and you don't want to.