A successful marriage has probably the best possible cost/trouble versus satisfaction/happyness ratio ever. You get a friend, a lover, a partner... all in the same body. We the people go for and into it unprepared, go figure! Except maybe Tom.
Pets have a very good cost/reward ratio, as long as you don´t have a pack, a Lion, or any other numerous, big or dangerous something.
Highest bet you can make in your life, other than betting your own life. The more people know about the sacrifices and risks involved, and the more they can control the Decision, the less children come to this World. On the other hand, it may bring you some of your very best moments, and it´s one of those few things that can make you feel like your life has some sense.
What can I say about cars? I´m so happy Miled got this one!
A mistress/playmate is a high cost, high satisfaction, high trouble, good and bad memories, lots of guilt and shame thingy ... unless you´re Andrei Kirilenko, who is allowed by his wife to have a story once per year.
Keep your friends close.
Trying to have your very own ideas is usually fun, cheap and productive.
Then there´s God above all: