I should have been...

...a secretary, but I wasn't the type.
...an art gallery owner, but I couldn't get the hang of it.
...a chimney sweeper, but it just didn't soot me.
...a doctor, but I wasn't patient enough.
...a plumber, but I was out of sink.
...a cricket player, but I couldn't catch on.
...a cardiologist, but I didn't have the heart.