Curtis McHale sums up why clients should wait for their favourite consultant.

Think of Gandalf (Lord of the Rings wizard if you don’t know). He was always running from one place to another. Someone always needed his help. He was a busy dude and couldn’t just take on every issue at the drop of a hat.

Any decent consultant is going to be like that. Really if you need more than a few hours of work, you should be expecting to wait.
— Wizards are Busy People by Curtis McHale

Never thought of myself as a wizard before though, but I do like the idea.