Putting a value on your own skills is never easy, especially when it comes to moving to a new firm.
Despite the fact that valuing a business is something that City types do fairly frequently, having a valuation placed on oneself is an uncomfortable experience, particularly when it's a relative stranger who will be assessing your worth on the other side of the negotiating table. Add to that an upbringing that tells you it's rude to talk about money and it's even worse.